Displays with Direct-lit Backlight Units

ABSTRACT

A display may have a pixel array such as a liquid crystal pixel array. The pixel array may be illuminated with backlight illumination from a direct-lit backlight unit. The backlight unit may include an array of light-emitting diodes on a printed circuit board. The backlight unit may include first, second, and third light spreading layers formed over the array of light-emitting diodes. A color conversion layer may be formed over the first, second, and third light spreading layers. First and second brightness enhancement films may be formed over the color conversion layer.

This application is a continuation of Non-Provisional Patent ApplicationNo. 17/409,467, filed Aug. 23, 2021, which claims the benefit ofProvisional Patent Application No. 63/175,723, filed Apr. 16, 2021,Provisional Patent Application No. 63/175,730, filed Apr. 16, 2021, andProvisional Patent Application No. 63/175,716, filed Apr. 16, 2021,which are hereby incorporated by reference herein in their entireties.

BACKGROUND

This relates generally to displays, and, more particularly, to backlitdisplays.

Electronic devices often include displays. For example, computers andcellular telephones are sometimes provided with backlit liquid crystaldisplays. Edge-lit backlight units have light-emitting diodes that emitlight into an edge surface of a light guide plate. The light guide platethen distributes the emitted light laterally across the display to serveas backlight illumination.

Direct-lit backlight units have arrays of light-emitting diodes thatemit light vertically through the display. If care is not taken,however, a direct-lit backlight may be bulky or may produce non-uniformbacklight illumination.

SUMMARY

A display may have a pixel array such as a liquid crystal pixel array.The pixel array may be illuminated with backlight illumination from adirect-lit backlight unit. The backlight unit may include an array oflight-emitting diodes on a printed circuit board.

The backlight unit may include first, second, and third light spreadinglayers formed over the array of light-emitting diodes. A colorconversion layer may be formed over the first, second, and third lightspreading layers. First and second brightness enhancement films may beformed over the color conversion layer.

The color conversion layer may include scattering dopants. The colorconversion layer may include an anti-static layer. The color conversionlayer may include a low-index layer. Yellow and/or clear ink may bepatterned on one of the brightness enhancement films.

One of the optical films in the backlight unit such as the colorconversion layer may be attached to a chassis along one edge of theprinted circuit board. Along the other edge of the printed circuitboard, electronic components may be formed in an inactive area.Standoffs may be included in the inactive area to protect the electroniccomponents. A stainless steel stiffener may wrap around the edge of theprinted circuit board with the electronic components.

The printed circuit board may have a high reflectivity to increase theefficiency of the display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an illustrative electronic device having adisplay in accordance with an embodiment.

FIG. 2 is a cross-sectional side view of an illustrative display inaccordance with an embodiment.

FIG. 3 is a top view of an illustrative light-emitting diode array for adirect-lit backlight unit in accordance with an embodiment.

FIG. 4 is a cross-sectional side view of an illustrative display havinga direct-lit backlight unit with three light spreading layers, a colorconversion layer, and two brightness enhancement films in accordancewith an embodiment.

FIG. 5 is a top view of an illustrative light spreading layer showingthe layout of pyramidal protrusions in the light spreading layer inaccordance with an embodiment.

FIG. 6 is a cross-sectional side view of illustrative light spreadinglayers that may be included in a backlight unit without any air gaps inaccordance with an embodiment.

FIGS. 7A-7C are top views of illustrative light spreading layers showinghow pyramidal protrusions in each light spreading layer may have thesame orientation in accordance with an embodiment.

FIGS. 8A-8C are top views of illustrative light spreading layers showinghow pyramidal protrusions in each light spreading layer may be rotatedrelative to the other light spreading layers in accordance with anembodiment.

FIGS. 9A-9C are top views of illustrative light spreading layers showinghow elongated protrusions in each light spreading layer may be rotatedrelative to the other light spreading layers in accordance with anembodiment.

FIG. 10 is a cross-sectional side view of an illustrative lightspreading layer showing how the apex angle of the protrusions in thelight spreading layer may be non-orthogonal in accordance with anembodiment.

FIG. 11 is a cross-sectional side view of an illustrative display havinga backlight with a light spreading layer that is attached directly toencapsulant of the LED array in accordance with an embodiment.

FIG. 12 is a graph of transmittance as a function of incidence angle forthe light spreading layer in FIG. 11 in accordance with an embodiment.

FIG. 13 is a cross-sectional side view of an illustrative colorconversion layer that includes scattering dopants in addition to colorconversion material (e.g., red and green phosphor, quantum dots,perovskite, etc.) in accordance with an embodiment.

FIG. 14 is a graph of brightness as a function of viewing angle for acolor conversion layer in accordance with an embodiment.

FIG. 15 is a cross-sectional side view of an illustrative colorconversion layer that includes an anti-static layer in accordance withan embodiment.

FIG. 16 is a cross-sectional side view of an illustrative colorconversion layer that includes a low-index layer in accordance with anembodiment.

FIG. 17 is a graph illustrating the color variation from alight-emitting diode cell in -Δv′ (negative delta v′) quantifying thebluishness of the light across the width of the light-emitting diodecell in accordance with an embodiment.

FIG. 18 is a graph illustrating how -Δv′ (negative delta v′),quantifying the bluishness of the light from a display, may vary acrossthe width of the display in accordance with an embodiment.

FIG. 19 is a top view of an illustrative display with more blue lightemitted in the edges of the display in accordance with an embodiment.

FIG. 20 is a top view of an illustrative brightness enhancement filmwith an edge portion having a yellow ink coating in accordance with anembodiment.

FIG. 21 is a cross-sectional side view of an illustrative brightnessenhancement film with a yellow ink coating on a lower surface inaccordance with an embodiment.

FIG. 22 is a rear view of an illustrative brightness enhancement filmwith a yellow ink coating on a lower surface in accordance with anembodiment.

FIG. 23 is a graph illustrating how the yellow ink coverage percentageon a brightness enhancement film may follow a curved profile to provideoutput light of a uniform color in accordance with an embodiment.

FIG. 24 is a cross-sectional side view of an illustrative brightnessenhancement film with a clear ink coating on a lower surface inaccordance with an embodiment.

FIG. 25 is a graph illustrating how the clear ink coverage percentage ona brightness enhancement film may be constant across the film inaccordance with an embodiment.

FIG. 26 is a graph illustrating how both yellow and clear ink may beincluded on a brightness enhancement film in accordance with anembodiment.

FIG. 27 is a top view of an illustrative backlight unit showing howelectronic components may be formed in an inactive area along one edgeof the printed circuit board in accordance with an embodiment.

FIG. 28 is a cross-sectional side view of an illustrative printedcircuit board having multiple highly reflective layers to improveefficiency in accordance with an embodiment.

FIG. 29 is a top view of an illustrative printed circuit board showinghow a light-emitting diode may be mounted to the printed circuit boardin a circular opening in a solder resist layer on the printed circuitboard in accordance with an embodiment.

FIG. 30 is a top view of an illustrative printed circuit board showinghow a light-emitting diode may be mounted to the printed circuit boardin a rectangular opening in a solder resist layer on the printed circuitboard in accordance with an embodiment.

FIG. 31 is a top view of an illustrative printed circuit board showinghow a solder resist layer may have a locally protruding portion thatextends towards the edge of the printed circuit board in accordance withan embodiment.

FIG. 32 is a cross-sectional side view of a light-emitting diode mountedto a printed circuit board showing how first and second passivationlayers may be formed on a lower surface of the light-emitting diode inaccordance with an embodiment.

FIG. 33 is a top view of an illustrative printed circuit board showinghow standoffs may be formed in the inactive area to protect electroniccomponents from damage in accordance with an embodiment.

FIG. 34 is a top view of an illustrative printed circuit board showinghow some electronic components in the inactive area may be surrounded onthree sides by encapsulant in accordance with an embodiment.

FIG. 35 is a rear view of an illustrative printed circuit board showinghow a conductive layer in the printed circuit board may be exposed alongthree edges of the printed circuit board in accordance with anembodiment.

FIG. 36 is a cross-sectional side view of an illustrative displayshowing various grounding structures in the display in accordance withan embodiment.

FIG. 37 is a cross-sectional side view of an illustrative displayshowing how a chassis in the display may have a shelf along an edge ofthe display that is attached to one of the optical films in thebacklight unit in accordance with an embodiment.

FIG. 38 is a top view of an illustrative backlight unit showing how thechassis may extend along only three edges of the printed circuit boardin accordance with an embodiment.

FIG. 39 is a cross-sectional side view of an illustrative displayshowing how a stainless steel stiffener may wrap around an edge of theprinted circuit board in accordance with an embodiment.

FIG. 40 is a diagram showing how the positions of light-emitting diodesin a backlight may be dithered to improve performance of the display inaccordance with an embodiment.

FIG. 41 is a top view of an illustrative light-emitting diode arrayshowing how the pitch between the light-emitting diodes in a backlightmay be reduced in a rounded corner area relative to non-rounded-cornerareas in accordance with an embodiment.

FIG. 42 is a cross-sectional side view of an illustrative displayshowing how a reflective layer may be patterned on encapsulant for thebacklight unit in accordance with an embodiment.

DETAILED DESCRIPTION

Electronic devices may be provided with backlit displays. The backlitdisplays may include liquid crystal pixel arrays or other displaystructures that are backlit by light from a direct-lit backlight unit. Aperspective view of an illustrative electronic device of the type thatmay be provided with a display having a direct-lit backlight unit isshown in FIG. 1 . Electronic device 10 of FIG. 1 may be a computingdevice such as a laptop computer, a computer monitor containing anembedded computer, a tablet computer, a cellular telephone, a mediaplayer, or other handheld or portable electronic device, a smallerdevice such as a wrist-watch device, a pendant device, a headphone orearpiece device, a device embedded in eyeglasses or other equipment wornon a user’s head, or other wearable or miniature device, a television, acomputer display that does not contain an embedded computer, a gamingdevice, a navigation device, an embedded system such as a system inwhich electronic equipment with a display is mounted in a kiosk orautomobile, equipment that implements the functionality of two or moreof these devices, or other electronic equipment.

As shown in FIG. 1 , device 10 may have a display such as display 14.Display 14 may be mounted in housing 12. Housing 12, which may sometimesbe referred to as an enclosure or case, may be formed of plastic, glass,ceramics, fiber composites, metal (e.g., stainless steel, aluminum,etc.), other suitable materials, or a combination of any two or more ofthese materials. Housing 12 may be formed using a unibody configurationin which some or all of housing 12 is machined or molded as a singlestructure or may be formed using multiple structures (e.g., an internalframe structure, one or more structures that form exterior housingsurfaces, etc.).

Housing 12 may have a stand, may have multiple parts (e.g., housingportions that move relative to each other to form a laptop computer orother device with movable parts), may have the shape of a cellulartelephone or tablet computer, and/or may have other suitableconfigurations. The arrangement for housing 12 that is shown in FIG. 1is illustrative.

Display 14 may be a touch screen display that incorporates a layer ofconductive capacitive touch sensor electrodes or other touch sensorcomponents (e.g., resistive touch sensor components, acoustic touchsensor components, force-based touch sensor components, light-basedtouch sensor components, etc.) or may be a display that is nottouch-sensitive. Capacitive touch screen electrodes may be formed froman array of indium tin oxide pads or other transparent conductivestructures.

Display 14 may include an array of pixels 16 formed from liquid crystaldisplay (LCD) components or may have an array of pixels based on otherdisplay technologies. A cross-sectional side view of display 14 is shownin FIG. 2 .

As shown in FIG. 2 , display 14 may include a pixel array such as pixelarray 24. Pixel array 24 may include an array of pixels such as pixels16 of FIG. 1 (e.g., an array of pixels having rows and columns of pixels16). Pixel array 24 may be formed from a liquid crystal display module(sometimes referred to as a liquid crystal display or liquid crystallayers) or other suitable pixel array structures. A liquid crystaldisplay for forming pixel array 24 may, as an example, include upper andlower polarizers, a color filter layer and a thin-film transistor layerinterposed between the upper and lower polarizers, and a layer of liquidcrystal material interposed between the color filter layer and thethin-film transistor layer. Liquid crystal display structures of othertypes may be used in forming pixel array 24, if desired.

During operation of display 14, images may be displayed on pixel array24. Backlight unit 42 (which may sometimes be referred to as abacklight, backlight layers, backlight structures, a backlight module, abacklight system, etc.) may be used in producing backlight illumination45 that passes through pixel array 24. This illuminates any images onpixel array 24 for viewing by a viewer such as viewer 20 who is viewingdisplay 14 in direction 22.

Backlight unit 42 may include a plurality of optical films 26 formedover light-emitting diode array 36. Light-emitting diode array 36 maycontain a two-dimensional array of light sources such as light-emittingdiodes 38 that produce backlight illumination 45. Light-emitting diodes38 may, as an example, be arranged in rows and columns and may lie inthe X-Y plane of FIG. 2 . Light-emitting diodes 38 may be mounted onprinted circuit board 50 (sometimes referred to as substrate 50) and maybe encapsulated by encapsulant 52 (sometimes referred to as transparentencapsulant 52, encapsulant slab 52, etc.). The slab of encapsulant 52may be formed continuously across the LED array and may have a planarupper surface.

Light-emitting diodes 38 may be controlled in unison by controlcircuitry in device 10 or may be individually controlled (e.g., toimplement a local dimming scheme that helps improve the dynamic range ofimages displayed on pixel array 24). The light produced by eachlight-emitting diode 38 may travel upwardly along dimension Z throughoptical films 26 before passing through pixel array 24.

Optical films 26 may include films such as one or more light spreadinglayers 28, color conversion layer 34, one or more brightness enhancementfilms 44 (sometimes referred to as collimating layers 44), and/or otheroptical films.

Light-emitting diodes 38 may emit light of any suitable color (e.g.,blue, red, green, white, etc.). With one illustrative configurationdescribed herein, light-emitting diodes 38 emit blue light. To helpprovide uniform backlight across backlight unit 42, light fromlight-emitting diodes 38 may be spread by light spreading layer 28. Thelight from the at least one light spreading layer 28 then passes throughcolor conversion layer 34 (which may sometimes be referred to as aphotoluminescent layer).

Color conversion layer 34 may convert the light from LEDs 38 from afirst color to a different color. For example, when the LEDs emit bluelight, color conversion layer 34 may include a phosphor layer (e.g., alayer of white phosphor material or other photoluminescent material)that converts blue light into white light. If desired, otherphotoluminescent materials may be used to convert blue light to light ofdifferent colors (e.g., red light, green light, white light, etc.). Forexample, one layer 34 may have a phosphor layer that includes quantumdots that convert blue light into red and green light (e.g., to producewhite backlight illumination that includes, red, green, and bluecomponents, etc.). Configurations in which light-emitting diodes 38 emitwhite light (e.g., so that layer 34 may be omitted, if desired) may alsobe used.

By the time light from light-emitting diodes 38 reaches the one or morebrightness enhancement films 44, the light has been converted from blueto white and has been homogenized (e.g., by the light spreading layer).Brightness enhancement films 44 may then collimate off-axis light toincrease the brightness of the display for a viewer viewing the displayin direction 22.

FIG. 3 is a top view of an illustrative light-emitting diode array forbacklight 42. As shown in FIG. 3 , light-emitting diode array 36 maycontain rows and columns of light-emitting diodes 38. Eachlight-emitting diode 38 may be associated with a respective cell (tilearea) 38C. The length D of the edges of cells 38C may be 2 mm, 18 mm,1-10 mm, 1-4 mm, 10-30 mm, more than 5 mm, more than 10 mm, more than 15mm, more than 20 mm, less than 25 mm, less than 20 mm, less than 15 mm,less than 10 mm, less than 1 mm, less than 0.1 mm, greater than 0.01 mm,greater than 0.1 mm, or any other desired size. If desired, hexagonallytiled arrays and arrays with light-emitting diodes 38 that are organizedin other suitable array patterns may be used. In arrays with rectangularcells, each cell may have sides of equal length (e.g., each cell mayhave a square outline in which four equal-length cell edges surround arespective light-emitting diode) or each cell may have sides ofdifferent lengths (e.g., a non-square rectangular shape). Theconfiguration of FIG. 3 in which light-emitting diode array 36 has rowsand columns of square light-emitting diode regions such as cells 38C ismerely illustrative.

If desired, each cell 38C may have a light source that is formed form anarray of light-emitting diode dies (e.g., multiple individuallight-emitting diodes 38 arranged in an array such as a 2 x 2 cluster oflight-emitting diodes at the center of each cell 38C). For example,light source 38′ in the leftmost and lowermost cell 38C of FIG. 3 hasbeen formed from a 2 x 2 array of light-emitting diodes 38 (e.g., fourseparate light-emitting diode dies). In general, each cell 38C mayinclude a light source 38′ with a single light-emitting diode 38, a pairof light-emitting diodes 38, 2-10 light-emitting diodes 38, at least twolight-emitting diodes 38, at least 4 light-emitting diodes 38, at leasteight light-emitting diodes 38, fewer than five light-emitting diodes38, or other suitable number of light-emitting diodes. Illustrativeconfigurations in which each cell 38C has a single light-emitting diode38 may sometimes be described herein as an example. This is, however,merely illustrative. Each cell 38C may have a light source 38 with anysuitable number of one or more light-emitting diodes 38. The diodes 38in light-emitting diode array 36 may be mounted on a printed circuitboard substrate (50) that extends across array 36 or may be mounted inarray 36 using other suitable arrangements.

As previously mentioned, more than one light spreading layer 28 and morethan one brightness enhancement film may be included in the opticalfilms 26 of the backlight unit 42. FIG. 4 is a cross-sectional side viewof an illustrative display having three light spreading layers and twobrightness enhancement films.

As shown in FIG. 4 , a first light spreading layer 28-1, a second lightspreading layer 28-2, and a third light spreading layer 28-3 are formedbetween light-emitting diode array 36 and color conversion layer 34.Each light spreading layer has a similar structure, with protrusions(sometimes referred to as prisms or light redirecting structures)extending from a substrate (base film). Light spreading layer 28-1includes protrusions 102-1 that extend from substrate 104-1. Lightspreading layer 28-2 includes protrusions 102-2 that extend fromsubstrate 104-2. Light spreading layer 28-3 includes protrusions 102-3that extend from substrate 104-3.

Substrates 104-1, 104-2, and 104-3 may sometimes be referred to as basefilm portions and may be formed from a transparent material such aspolyethylene terephthalate (PET) or any other desired material. Lightredirecting structures 102-1, 102-2, and 102-3 may be formed from thesame material as base film portions 104-1, 104-2, and 104-3 or may beformed from a different material than the base film portion. Differentmaterials may be used in each light spreading layer if desired or thelight spreading layers may be formed from the same material(s).

For each light spreading layer, the protrusions 102 may be formed in anarray across the light spreading layer. Each protrusion 102 (sometimesreferred to as light redirecting structure 102 or prism 102) may splitan incoming point light source into three or more points. Theprotrusions may have a pyramidal shape (e.g., with a square base andfour triangular faces that meet at a vertex), a triangular pyramidalshape (e.g., with a triangular base and three triangular faces that meetat a vertex), partial-cube shape (e.g., corner-cubes by three squarefaces that meet at a vertex), a tapered pyramid structure (where eachface of the pyramid has an upper portion and a lower portion that are atan angle relative to one another), or any other desired shape.Square-based pyramidal protrusions may split a point light source intofour points, whereas triangular pyramidal protrusions may split a pointlight source into three points.

FIG. 5 is a top view of light spreading layer 28-1 showing howprotrusions 102-1 may be arranged in an array. In this case, eachprotrusion has a pyramidal shape with a square base and four triangularfaces that meet at a vertex 106.

The example in FIGS. 4 and 5 of the light redirecting structures 102being formed from protrusions from a substrate is merely illustrative.In another possible arrangement, the light redirecting structures may beformed as recesses in the corresponding substrate film 104. The recessesmay have any desired shape (e.g., a square-based pyramidal shape, atriangular-based pyramidal shape, etc.). Additionally, the example inFIG. 4 of light redirecting structures 102 being formed on the lowersurface of the light redirecting layers is merely illustrative. Lightredirecting structures 102 may alternatively be formed on the uppersurface in one or more of the light redirecting layers.

Substrates 104-1, 104-2, and 104-3 in FIG. 4 may each have a matte uppersurface (e.g., the surface that is higher in the positive Z-directionmay be matte). The matte upper surface may mitigate undesiredreflections in the backlight unit.

Light spreading layer 28-3 (e.g., substrate 104-3 and/or prisms 102-3)may be formed from a diffusive material such that light travelling alongthe Z-axis is diffused by light spreading layer 28-3. In contrast, lightspreading layers 28-1 and 28-2 are not formed from diffusive material.In one arrangement, substrate 104-3 is formed from an entirely different(and more diffusive) material than substrate 104-2 and 104-1. In anotherpossible arrangement, substrates 104-1, 104-2, and 104-3 are formed fromthe same base material and substrate 104-3 includes an additive thatincreases the diffusion of substrate 104-3 relative to substrates 104-1and 104-2 (which do not include the diffusion-increasing additive).

As shown in FIG. 4 , color conversion layer 34 may include a phosphorlayer 40 (e.g., a layer of white phosphor material or otherphotoluminescent material) that converts blue light into white light. Ifdesired, other photoluminescent materials may be used to convert bluelight from LEDs 38 to light of different colors (e.g., red light, greenlight, white light, etc.). For example, phosphor layer 40 may includered quantum dots 112-R that convert blue light into red light and greenquantum dots 112-G that convert blue light into green light (e.g., toproduce white backlight illumination that includes, red, green, and bluecomponents, etc.).

In addition to phosphor layer 40, color conversion layer 34 may includea partially reflective layer 41. Partially reflective layer 41(sometimes referred to as a dichroic layer or dichroic filter layer) mayreflect all red and green light and partially reflect blue light, forexample. Partially reflective layer 41 therefore allows for some of theblue light to be recycled through optical films 26.

An additional film such as film 108 may also be included in the colorconversion layer. The additional film 108 (sometimes referred to as anoptical film, substrate, base film, etc.) may be formed from a polymermaterial (e.g., polyethylene terephthalate). Light redirectingstructures such as protrusions 102-4 may be formed on an upper surfaceof additional film 108. Protrusions 102-4 may have any one of thearrangements described above in connection with protrusions 102-1,102-2, and 102-3 (e.g., an array of pyramids as shown in FIG. 5 ). Lightredirecting structures 102-4 may be formed from the same material asfilm 108 or may be formed from a different material than the film 108.

In the example of FIG. 4 , a first brightness and enhancement film 44-1and a second brightness enhancement film 44-2 are included in thebacklight unit. Each brightness enhancement film has a similarstructure, with protrusions (sometimes referred to as prisms or lightredirecting structures) extending from a substrate (base film).Brightness enhancement film 44-1 includes protrusions 110-1 that extendfrom substrate 114-1. Brightness enhancement film 44-2 includesprotrusions 110-2 that extend from substrate 114-2.

Substrates 114-1 and 114-2 may sometimes be referred to as base filmportions and may be formed from a transparent material such aspolyethylene terephthalate (PET) or any other desired material. Lightredirecting structures 110-1 and 110-2 may be formed from the samematerial as base film portions 114-1 and 114-2 or may be formed from adifferent material than the base film portions. Different materials maybe used in each brightness enhancement film if desired or the lightspreading layers may be formed from the same material(s).

In each brightness enhancement film, the protrusions 110 may extend instrips across the light spreading layer. For example, protrusions 110-1may be elongated, parallel protrusions (sometimes referred to as ridges)that extend along a longitudinal axis across the layer (e.g., parallelto the Y-axis in FIG. 4 ). Protrusions 110-2 may have a similarstructure as protrusions 110-1 (with elongated, parallel protrusionsextending across the brightness enhancement film). Protrusions 110-2 maybe rotated (e.g., by 90°) relative to the protrusions 110-1.

The example in FIG. 4 of the light redirecting structures 110 beingformed from protrusions from a substrate is merely illustrative. Inanother possible arrangement, the light redirecting structures 110 maybe formed as recesses (e.g., elongated recesses) in the correspondingsubstrate film 114. Additionally, the example in FIG. 4 of lightredirecting structures 110 being formed on the upper surface of thebrightness enhancement films is merely illustrative. Light redirectingstructures 110 may alternatively be formed on the lower surface in oneor more of the brightness enhancement films.

In FIG. 4 , each adjacent pair of optical films may be separated by anair gap. The air gap may provide a refractive index difference as lightenters and exits each optical film, ensuring the light from LEDs 38 isspread by the light spreading layers 28 (e.g., via refraction and/ordiffraction).

Alternatively, instead of including air gaps between light spreadinglayers 28-1, 28-2, and 28-3, a low-index sheet may be incorporatedbetween each adjacent light spreading layer. FIG. 6 is a cross-sectionalside view of light spreading layers that may be included in thebacklight unit (e.g., in the backlight unit of FIG. 4 ). Similar to asin FIG. 4 , the light spreading layers in FIG. 6 include a first lightspreading layer 28-1, a second light spreading layer 28-2, and a thirdlight spreading layer 28-3. Each light spreading layer has a similarstructure, with protrusions (sometimes referred to as prisms or lightredirecting structures) extending from a substrate. Light spreadinglayer 28-1 includes protrusions 102-1 that extend from substrate 104-1.Light spreading layer 28-2 includes protrusions 102-2 that extend fromsubstrate 104-2. Light spreading layer 28-3 includes protrusions 102-3that extend from substrate 104-3.

However, instead of an air gap separating each light spreading layer (asin FIG. 4 ), the light spreading layers in FIG. 6 are separated by alow-index layer and a diffusive adhesive layer. As shown in FIG. 6 , adiffusive adhesive layer 116-1 and low-index layer 118-1 are interposedbetween light spreading layers 28-1 and 28-2. In the arrangement of FIG.6 , adhesive layer 116-1 is interposed between (and directly contacts)base film portion 104-1 and low-index layer 118-1 whereas low-indexlayer 118-1 is interposed between (and directly contacts) adhesive layer116-1 and protrusions 102-2. Low-index layer 118-1 may conform to anddirectly contact protrusions 102-2.

As shown in FIG. 6 , a diffusive adhesive layer 116-2 and low-indexlayer 118-2 are interposed between light spreading layers 28-2 and 28-3.In the arrangement of FIG. 6 , adhesive layer 116-2 is interposedbetween (and directly contacts) base film portion 104-2 and low-indexlayer 118-2 whereas low-index layer 118-2 is interposed between (anddirectly contacts) adhesive layer 116-2 and protrusions 102-3. Low-indexlayer 118-2 may conform to and directly contact protrusions 102-3.

The low-index layers 116-1 and 116-2 may be formed from a transparentmaterial having an index of refraction that is less than 1.4, less than1.3, less than 1.2, less than 1.1, between 1.1 and 1.3, or any otherdesired index of refraction. Protrusions 102-2 and 102-3 (as well ascorresponding base film portions 104-2 and 104-3) may have refractiveindices that are greater than 1.4, greater than 1.5, greater than 1.6,greater than 1.7, between 1.6 and 1.7, or any other desired index ofrefraction. The difference in refractive index between low-index layer118-1 and protrusions 102-2 may be greater than 0.2, greater than 0.3,greater than 0.4, greater than 0.5, greater than 0.6, between 0.3 and0.6, between 0.4 and 0.5, or any other desired refractive indexdifference. This refractive index difference ensures that protrusions102-2 spread light received from the LEDs 38. The difference inrefractive index between low-index layer 118-2 and protrusions 102-3 maybe greater than 0.2, greater than 0.3, greater than 0.4, greater than0.5, greater than 0.6, between 0.3 and 0.6, between 0.4 and 0.5, or anyother desired refractive index difference. This refractive indexdifference ensures that protrusions 102-3 spread light received from theLEDs 38.

The adhesive layers 116-1 and 116-2 may be formed from a transparentmaterial (e.g., having a transparency of greater than 95%, greater than99%, etc.). The adhesive layers may optionally be diffusive. Theadhesive layers may be formed from a diffusive material and/or mayinclude an additive that increases the diffusion of the adhesive layer.The adhesive layers 116-1 and 116-2 may be pressure sensitive adhesive(PSA) or liquid optically clear adhesive (LOCA), as examples.

Having the light spreading layers integrated as in FIG. 6 may improvethe buckling and wrinkle resistance of the light spreading layers whilestill maintaining satisfactory light spreading performance (due to thepresence of the low-index layers).

In one possible arrangement, light spreading layers 28-1, 28-2, and 28-3may have light spreading layers with the same orientation. FIGS. 7A-7Care top views of light spreading layers 28-1, 28-2, and 28-3 that may beincluded in backlight unit 42 in FIG. 4 . As shown in FIG. 7A, lightspreading layer 28-1 has protrusions 102-1 (e.g., pyramidal protrusions)that have bases with edges that are parallel to the X-axis and theY-axis. Light spreading layer 28-2 in FIG. 7B has protrusions 102-2 withthe same alignment/orientation as light spreading layer 28-1.Protrusions 102-2 may be pyramidal protrusions with edges (e.g., attheir bases) that are parallel to the X-axis and Y-axis. Light spreadinglayer 28-3 in FIG. 7C has protrusions 102-3 with the samealignment/orientation as light spreading layer 28-1 and light spreadinglayer 28-2. Protrusions 102-3 may be pyramidal protrusions with edges(e.g., at their bases) that are parallel to the X-axis and Y-axis.

Instead of protrusions 102-1, 102-2, and 102-3 having the same alignment(as in FIGS. 7A-7C), the light spreading layers may instead haveprotrusions with different alignments. FIGS. 8A-8C show an arrangementof this type. FIGS. 8A-8C are top views of light spreading layers 28-1,28-2, and 28-3 that may be included in backlight unit 42 in FIG. 4 . Asshown in FIG. 8A, light spreading layer 28-1 has protrusions 102-1(e.g., pyramidal protrusions) that have bases with edges that areparallel to the X-axis and the Y-axis. However, light spreading layer28-2 in FIG. 8B has protrusions 102-2 with a different alignment aslight spreading layer 28-1. Protrusions 102-2 may be pyramidalprotrusions with edges (e.g., at their bases) that are rotated by angle120 relative to the edges of protrusions 102-1 (which are parallel tothe X-axis and Y-axis). Angle 120 may be, for example, 30 degrees,between 20 degrees and 40 degrees, less than 45 degrees, greater than 10degrees, between 25 and 35 degrees, or any other desired angle.

Light spreading layer 28-3 in FIG. 8C has protrusions 102-3 with adifferent alignment as light spreading layers 28-1 and 28-2. Protrusions102-3 may be pyramidal protrusions with edges (e.g., at their bases)that are rotated by angle 122 relative to the edges of protrusions 102-1(which are parallel to the X-axis and Y-axis). Angle 122 may be, forexample, 60 degrees, between 50 degrees and 70 degrees, greater than 45degrees, less than 80 degrees, between 55 and 65 degrees, or any otherdesired angle. The difference between angle 120 and angle 122 (which isalso equal to the angle between the edges of protrusions 102-2 andprotrusions 102-3) may be 30 degrees, between 20 degrees and 40 degrees,less than 45 degrees, greater than 10 degrees, between 25 and 35degrees, or any other desired angle.

Rotating the protrusions of each light spreading layer relative to theprotrusions of the other light spreading layers may improve the lightmixing provided by light spreading layers 28-1, 28-2, and 28-3.

In some cases, light spreading layers 28-1, 28-2, and 28-3 may includeelongated protrusions that extend along an axis across the lightspreading layer. Each elongated protrusion may have the samecross-sectional shape (e.g., a triangular cross-section, a semi-circularcross-section, or any other desired shape) across its length. Theseprotrusions may only spread light across one dimension. FIGS. 9A-9C aretop views of light spreading layers 28-1, 28-2, and 28-3 that may beincluded in backlight unit 42 in FIG. 4 . For example, in FIG. 9A,elongated protrusions 102-1 extend parallel to the X-axis. Theseprotrusions therefore spread light along the Y-direction (e.g., in thepositive and negative Y-direction). In contrast, the pyramidalprotrusions (e.g., in FIG. 7A), spread light along two directions (e.g.,both in the positive and negative X-direction and in the positive andnegative Y-direction).

When light spreading layers 28-1, 28-2, and 28-3 include elongatedprotrusions, the alignment of the protrusions in each light spreadinglayer may be rotated relative to the other light spreading layers. Asshown in FIG. 9A, light spreading layer 28-1 has protrusions 102-1(e.g., elongated protrusions) that have bases with edges that areparallel to the Y-axis. However, light spreading layer 28-2 in FIG. 9Bhas protrusions 102-2 with a different alignment/orientation as lightspreading layer 28-1. Protrusions 102-2 may be elongated protrusionswith edges (e.g., at their bases) that are rotated by angle 120 relativeto the edges of protrusions 102-1 (which are parallel to the Y-axis).Angle 120 may be, for example, 60 degrees, between 50 degrees and 70degrees, greater than 45 degrees, less than 80 degrees, between 55 and65 degrees, or any other desired angle.

Light spreading layer 28-3 in FIG. 9C has protrusions 102-3 with adifferent alignment/orientation as light spreading layers 28-1 and 28-2.Protrusions 102-3 may be elongated protrusions with edges (e.g., attheir bases) that are rotated by angle 122 relative to the edges ofprotrusions 102-1 (which are parallel to the Y-axis). Angle 122 may be,for example, 120 degrees, between 110 degrees and 130 degrees, greaterthan 90 degrees, less than 180 degrees, between 100 and 140 degrees, orany other desired angle. The difference between angle 120 and angle 122(which is also equal to the angle between the edges of protrusions 102-2and protrusions 102-3) may be 60 degrees, between 50 degrees and 70degrees, greater than 45 degrees, less than 80 degrees, between 55 and65 degrees, or any other desired angle.

Rotating the elongated protrusions of each light spreading layerrelative to the elongated protrusions of the other light spreadinglayers may improve the light mixing provided by light spreading layers28-1, 28-2, and 28-3.

As previously discussed, the angle between the protrusions of each filmin FIGS. 8A-8C may be 30 degrees. This value may be obtained by dividing90 degrees by the number of light spreading layers. In other words, theangle between each adjacent pair of light spreading layers in FIGS.8A-8C may be equal to 90 degrees divided by the total number of lightspreading layers. This example is merely illustrative. In anotherpossible arrangement, the angle between each adjacent pair of lightspreading layers may be equal to 180 degrees divided by the total numberof light spreading layers. For example, the angle between theprotrusions of each film in FIGS. 9A-9C may be 60 degrees. This valuemay be obtained by dividing 180 degrees by the number of light spreadinglayers. In other words, the angle between each adjacent pair of lightspreading layers in FIGS. 9A-9C may be equal to 180 degrees divided bythe total number of light spreading layers.

FIG. 10 is a cross-sectional side view of an illustrative lightspreading layer in backlight unit 42. As shown, whether the protrusions102-1 are formed from a pyramidal structure (as in FIGS. 7A-7C and FIGS.8A-8C) or an elongated structure (e.g., having a triangularcross-sectional shape), the protrusions 102-1 are defined by an apexangle 124. Apex angle may be equal to 90 degrees or may be equal to anon-orthogonal angle. Apex angle 124 may be between 75 degrees and 105degrees, between 80 degrees and 89 degrees, between 83 degrees and 87degrees, a non-orthogonal angle between 75 degrees and 105 degrees, orany other desired angle.

FIG. 11 is a cross-sectional side view of an illustrative display havinga backlight with a light spreading layer 28 that is attached directly toencapsulant of the LED array for the backlight. As shown in FIG. 11 ,light spreading layer 28 is formed on an upper surface of encapsulant 52for LED array 36. The light spreading layer 28 may be in direct contactwith the upper surface of encapsulant 52 or an optically clear adhesivelayer may attach the light spreading layer directly to the upper surfaceof encapsulant (e.g., the adhesive layer may have a first surface indirect contact with the light spreading layer 28 and a second surface indirect contact with the encapsulant 52).

In FIG. 11 , light spreading layer 28 may have a low transmission (andhigh reflectivity) for on-axis light (e.g., light that is parallel tothe Z-axis) and an increasingly high transmission with increasinglyhigh-angled off-axis light (e.g., light that is angled away from theZ-axis). Consequently, on-axis light rays such as on-axis light 126(that are emitted parallel to the surface normal of the display andtherefore considered ‘on-axis’) that are emitted in the positiveZ-direction are reflected in the negative Z-direction by light spreadinglayer 28. Meanwhile, off-axis light rays (that deviate from the surfacenormal of the display by a large angle) such as off-axis light 128 maybe transmitted by light spreading layer 28. Light spreading layer 28 maymitigate hotspots caused by LEDs 38 by reflecting on-axis light fromLEDs 38 while transmitting off-axis light from LEDs 38.

The varying transmission profile as a function of entry angle may beachieved using a plurality of layers with different refractive indices.For example, layers L1 and L2 may alternate throughout the lightspreading layer 28. There may be any desired number of layers of eachtype in the light spreading layer (e.g., more than two, more than five,more than ten, more than thirty, more than fifty, more than one hundred,more than two hundred, less than two hundred, between fifty and onehundred and fifty, etc.). Layers L1 and L2 may be formed from polymermaterials that have a refractive index difference. For example, layer L1may have a refractive index of less than 1.55 whereas layer L2 may havea refractive index of more than 1.65. The difference in refractive indexbetween layers L1 and L2 may be more than 0.1, more than 0.15, more than0.2, more than 0.25, between 0.15 and 0.25, between 0.1 and 0.3, or anyother desired magnitude.

FIG. 12 is a graph showing the transmission profile of light spreadinglayer 28 as a function of the incidence angle of light received by thelight spreading layer. As shown, transmittance may be at a minimum at anon-axis (0 degree) angle (e.g., ray 126 in FIG. 11 ). At on-axis entryangles, transmittance may be less than 10%, less than 5%, less than 3%,less than 2%, etc. At on-axis entry angles, the light spreading layermay reflect more than 90% of light, more than 95% of light, more than97% of light, more than 98% of light, etc. As the incidence angle oflight increases in either off-axis direction (e.g., positive off-axisdirections or negative off-axis directions), transmittance through thelight spreading layer increases (and, accordingly, reflectancedecreases). In other words, transmittance through the light spreadinglayer increasing with increasing deviation of the angle of incidencefrom the surface normal. The shape of the profile shown in FIG. 12 ismerely illustrative. In general, the profile may have any desired shape.

Light spreading layer 28 in FIG. 11 may be formed with a diffuse topsurface 28-T that includes texture / roughness to help mitigate totalinternal reflection off of the upper surface and spread the light thatexits the light spreading layer across a wider range of viewing angles.

The layers above light spreading layer 28 in FIG. 11 may be the same asin FIG. 4 (e.g., with a color conversion layer 34, brightnessenhancement films 44-1 and 44-2, and pixel array 24).

FIG. 13 is a cross-sectional side view of an illustrative colorconversion layer 34 with scattering dopants for increasing the amount ofoff-axis blue light. The color conversion layer 34 in FIG. 13 may beused in any of the backlight arrangements herein (e.g., in the backlightof FIG. 4 , the backlight of FIG. 11 , etc.). As shown in the insetportion of FIG. 13 , red quantum dots 112-R output light in a randomdirection (e.g., the direction that red light is output is notcorrelated to the direction that blue light is received). Similarly,green quantum dots 112-G output light in a random direction (e.g., thedirection that green light is output is not correlated to the directionthat blue light is received). To make the emission direction of bluelight more random (and therefore equalize the off-axis emission of bluelight to the off-axis emission of red and green light), scatteringdopants 130 may be included in the phosphor layer. Scattering dopants130 may elastically scatter blue light. This means that no energy islost when the scattering dopants 130 receive blue light and that thewavelength of the light is not changed by the scattering dopants.However, the scattering dopants randomize the direction of the bluelight. The blue light will be scattered by the scattering dopants whilethe red and green light will tend not to be scattered by the scatteringdopants. Consequently, the distribution of red, blue, and green lightmay be equalized both on-axis and off-axis.

The average diameter of the scattering dopants may be between 5 and 20nanometers, less than 500 nanometers, less than 100 nanometers, lessthan 50 nanometers, less than 20 nanometers, more than 5 nanometers,more than 1 nanometer, or any other desired diameter. The averagediameter of quantum dots 112-R and 112-G may be more than 500nanometers, more than 1 micron, more than 2 microns, between 1 and 3microns, less than 5 microns, or any other desired diameter.

The quantum dots 112-R and 112-G as well as scattering dopants 130 maybe distributed in a resin 132 (sometimes referred to as host resin 132).Resin 132 may have an index of refraction of less than 1.5, less between1.45 and 1.55, less than 1.6, less than 1.55, greater than 1.4, between1.4 and 1.6, or any other desired index of refraction. To achieve thedesired scattering using the scattering dopants, the scattering dopantsmay be formed using a transparent material that has an index ofrefraction that is greater than 1.5, greater than 1.55, greater than1.6, greater than 1.65, greater than 1.7, between 1.6 and 1.7, between1.55 and 1.7, or any other desired index of refraction. The differencein refractive index between resin 132 and scattering dopants 130 may begreater than 0.05, greater than 0.1, greater than 0.15, greater than0.2, between 0.1 and 0.2, between 0.15 and 0.2, or any other desiredmagnitude.

In general, the scattering dopants may be formed from any desiredmaterial (e.g., silicone, melamine, etc.). As one example, thescattering dopants may be formed from melamine (C₃H₆N₆, having an indexof refraction of 1.66) whereas the resin 132 may have a refractive indexof 1.49. The density of scattering dopants 130 within the phosphor layermay be less than 10 g/m³, less than 5 g/m³, less than 3 g/m³, less than2 g/m³, more than 1 g/m³, more than 2 g/m³, more than 3 g/m³, between 1g/m³ and 3 g/m³, between 1.5 g/m³ and 2.5 g/m³, between 1 g/m³ and 5g/m³, or any other desired density.

It should be noted that the example of including red and green quantumdots in the color conversion layer is merely illustrative. In general,any desired red/green color conversion materials may be included (e.g.,red and green phosphor, quantum dots, perovskite, etc.).

FIG. 14 is graph of the blue light brightness of the phosphor layer 40as a function of viewing angle. Both profiles 134 and 136 reflect thescattering profile of blue light (e.g., at 450 nanometers or anotherdesired wavelength) exiting the phosphor layer when the phosphor layerreceives collimated blue light.

Profile 134 shows the brightness curve for a phosphor layer 40 that doesnot include scattering dopants. As shown, the brightness peaks around 0degrees with a drop off to low brightness levels at off-axis viewingangles. Profile 136 shows the brightness curve for a phosphor layer 40that does include scattering dopants (e.g., the phosphor layer of FIG.13 ). As shown, the presence of the scattering dopants increases thebreadth of the profile, such that the brightness is higher at off-axisviewing angles relative to profile 134. With the scattering dopants(e.g., profile 136), the blue light has a sufficiently high brightnessat off-axis viewing angles to match the brightness curves of green lightand red light that are also emitted from the phosphor layer. Whenscattering dopants 130 are included in the phosphor layer, the light istherefore uniform across a wide range of viewing angles (since the red,blue, and green brightness have similar profiles). Without scatteringdopants 130, the light may not be uniform at off-axis viewing angles(due to a relatively low amount of blue light being present compared tored light and green light).

In FIG. 14 , profile 136 (for a color conversion layer with scatteringdopants) may have a first width at 75% of the peak brightness (which isat an on-axis, 0 degree angle), a second width at 50% of the peakbrightness, and a third width at 25% of the peak brightness. The firstwidth may be greater than 20 degrees, greater than 25 degrees, greaterthan 30 degrees, less than 35 degrees, between 20 degrees and 30degrees, between 25 degrees and 30 degrees, etc. The second width may begreater than 40 degrees, greater than 45 degrees, greater than 50degrees, less than 60 degrees, between 40 degrees and 60 degrees,between 45 degrees and 55 degrees, etc. The third width may be greaterthan 60 degrees, greater than 70 degrees, greater than 80 degrees, lessthan 100 degrees, less than 90 degrees, between 60 degrees and 100degrees, between 75 degrees and 85 degrees, etc. As one illustrativeexample, the first width may be between 25 degrees and 30 degrees, thesecond width may be between 45 degrees and 55 degrees, and the thirdwidth may be between 75 degrees and 85 degrees. The shapes of profiles134 and 136 shown in FIG. 14 are merely illustrative. In general, theprofiles may have any desired shapes.

To mitigate electric static charge within color conversion layer 34, thecolor conversion layer 34 may include an embedded anti-static layer.FIG. 15 is a cross-sectional side view of an illustrative colorconversion layer 34 that includes an anti-static layer. The colorconversion layer 34 in FIG. 15 may be used in any of the backlightarrangements herein (e.g., in the backlight of FIG. 4 , the backlight ofFIG. 11 , etc.). As shown in FIG. 15 , anti-static layer 138 may beinterposed between film 108 and protrusions 102-4. Without anti-staticlayer 138, the optical film formed by base film 108 and protrusions102-4 may generate strong electric charge during the manufacturingprocess. Resin 132 in phosphor layer 40 may be repelled by the electricstatic charge on the bottom surface 108-B of film 108. This may causecoating uniformity issues (e.g., visible dimple defects) when film 108is laminated to phosphor layer 40.

Anti-static layer 138 is formed on the top surface 108-T of the basefilm 108. The anti-static layer 138 may be formed from any desiredanti-static material having a high transparency (e.g., greater than 90%,greater than 95%, greater than 99%, etc.). Without anti-static layer138, the static decay time at bottom surface 108-B of film 108 may beundesirably high (e.g., greater than 1 minute). With anti-static layer138 present, the static decay time at bottom surface 108-B of film 108may be less than 10 seconds, less than 5 seconds, less than 2 seconds,less than 1 second, less than 0.5 seconds, less than 0.3 seconds, lessthan 0.2 seconds, between 0.1 and 1 seconds, etc.

The anti-static layer 138 may be interposed between film 108 and anydesired type of protrusions 102-4 (e.g., pyramidal protrusions,elongated protrusions, etc.). In another possible arrangement,protrusions 102-4 may be omitted from the color conversion layer andanti-static layer 138 may be the upper-most layer in the colorconversion layer. The anti-static layer may also be formed at otherdesired positions within the backlight if desired.

To mitigate color breakup caused by a brightness difference between bluelight and red/green light, color conversion layer 134 may include alow-index layer between the phosphor layer 40 and film 108. Without thelow-index layer (e.g., in an embodiment of the type shown in FIGS. 13and 15 ), the combination of base film portion 108, phosphor layer 40,and partially reflective layer 41 may (for some of the light)effectively form a waveguide that guides light via total internalreflection. This phenomenon may impact the red and green light more thanthe blue light, leading to color breakup.

FIG. 16 is a cross-sectional side view of an illustrative colorconversion layer 34 that includes a low-index layer to mitigate colorbreakup. The color conversion layer 34 in FIG. 16 may be used in any ofthe backlight arrangements herein (e.g., in the backlight of FIG. 4 ,the backlight of FIG. 11 , etc.). As shown in FIG. 16 , low-index layer140 (sometimes referred to as optical decoupling layer) may beinterposed between phosphor layer 40 and base film portion 108.Low-index layer 140 may be formed from a transparent material having anindex of refraction that is less than 1.4, less than 1.3, less than 1.2,less than 1.1, between 1.0 and 1.3, or any other desired index ofrefraction. The difference in refractive index between low-index layer140 and base film 108 may be greater than 0.2, greater than 0.3, greaterthan 0.4, greater than 0.5, greater than 0.6, between 0.3 and 0.6,between 0.4 and 0.5, or any other desired refractive index difference.The difference in refractive index between low-index layer 140 and resin132 of phosphor layer 40 may be greater than 0.2, greater than 0.3,greater than 0.4, greater than 0.5, greater than 0.6, between 0.3 and0.6, between 0.4 and 0.5, or any other desired refractive indexdifference.

Low-index layer 140 therefore effectively optically decouples base filmportion 108 and phosphor layer 40. This breaks the aforementionedwaveguide effect and mitigates color breakup in the color conversionlayer 34. Additionally, the presence of the additional low-index layermay create additional light recycling, thus improving the point sourcefunction (PSF) width of light exiting the color conversion layer.

In addition to or instead of having low-index layer 140 between phosphorlayer 40 and base film portion 108, a low-index layer may beincorporated at other locations within the color conversion layer (e.g.,between base film portion 108 and protrusions 102-4).

Returning to FIG. 3 which shows LED cells 38C, the light from the edgeof a cell 38C tends to have been recycled more than light emitted fromthe center of the cell. Therefore, light from the edge of the cell maybe less blue than light from the middle of the cell. FIG. 17 is a graphillustrating this effect. As shown by curve 142 in FIG. 17 , light fromthe center of cell is bluer than light from the edges of the cell. Theshape of the profile shown in FIG. 17 is merely illustrative. Ingeneral, the profile may have any desired shape.

Within the display (e.g., the middle of the display), light from a givencell is mixed with light from neighboring cells to produce display lightof a uniform color (with a particular amount of blue light). However, atthe edges of the display, there may be a shortage of yellow light(because at an edge, yellow light from a neighboring cell is absent atthe border). This makes light from the edge of the display bluer thanlight from the middle of the display. This effect is shown in the graphof FIG. 18 . As shown by curve 144, light from the edge of the displayis bluer than light from the middle of the display. Each mark along theX-axis indicates the border of a respective cell 38C. As shown, lightexiting from the two cells closest to the edge of the display is bluerthan the remaining cells in the display. This example is merelyillustrative, and light exiting from any desired number of cells may bebluer than the remaining cells in the display depending on the specificdisplay design. The curve shown in FIG. 18 is merely illustrative andmay have a different shape if desired.

FIG. 19 is a top view of an illustrative display showing how the lightexiting from an edge region 14E may be bluer than light exiting from acentral portion 14C of the display. The blue edge region 14E may extendaround the periphery of the display.

To mitigate the color non-uniformity of the emitted light from thedisplay, a yellow ink pattern may be applied to the edges of one or bothof the brightness enhancement films 44 in the backlight unit. FIG. 20 isa top view of the rear surface (i.e., a rear view) of a brightnessenhancement film 44 such as brightness enhancement film 44-1 in FIG. 4or FIG. 11 . As shown in FIG. 20 , brightness enhancement film 44-1 mayhave a ring-shaped edge region 44E that extends around the periphery ofthe brightness enhancement film 44-1 (which has approximately the samefootprint as the display). A yellow ink 146 may be formed in edge region44E to compensate for the otherwise bluish border of the display. Yellowink 146 may be patterned on a lower surface of the brightnessenhancement film, as an example.

FIG. 21 is a cross-sectional side view of brightness enhancement film44-1 with yellow ink patterned on a lower surface of base film portion114-1. In this example, brightness enhancement film 44-1 has protrusions110-1 (sometimes referred to as prisms or light redirecting structures)extending from a substrate 114-1. Substrate 114-1 may sometimes bereferred to as base film portion and may be formed from a transparentmaterial such as polyethylene terephthalate (PET) or any other desiredmaterial. Light redirecting structures 110-1 may be formed from the samematerial as base film portion 114-1 or may be formed from a differentmaterial than the base film portion. The protrusions 110-1 may extend instrips across the light spreading layer. For example, protrusions 110-1may be elongated, parallel protrusions (sometimes referred to as ridges)that extend along a longitudinal axis across the layer (e.g., parallelto the Y-axis in FIG. 21 ).

Yellow ink dots 146 may be formed on a bottom surface 114-B of substrate114-1. In other words, the yellow ink dots are formed on the oppositesurface of substrate 114-1 as protrusions 110-1. Forming the yellow inkdots on the flat bottom surface 114-B of the substrate 114-1 may beeasier from a manufacturing perspective than forming the yellow ink dotsdirectly on protrusions 110-1. The yellow ink dots may absorb blue lightand therefore compensate for the blue tint in the border of the display.As shown in FIG. 21 , the density of the yellow ink dots may decreasewith increasing separation from the edge of the brightness-enhancementfilm. The density of the yellow ink dots may follow a profile thatmirrors the profile of the bluishness of the display (to optimallycompensate the display at different positions).

FIG. 22 is a top view of the bottom surface 114-B of substrate 114-1 inbrightness enhancement film 44-1. FIG. 22 shows how yellow ink dots 146may be distributed across the brightness enhancement film. As shown inFIG. 22 , the density of the yellow ink dots may decrease withincreasing separation from the edge of the brightness-enhancement film.

FIG. 23 is a graph of the yellow ink coverage percentage as a functionof position across the brightness enhancement film. As shown by profile148, the yellow ink coverage percentage (e.g., the total percentage ofeach unit area of surface 114-B that is covered with yellow ink) has amaximum P₁ at the edge of the brightness enhancement film. The coveragepercentage then decreases with increasing separation from the edge ofthe brightness enhancement film according to a curved profile. Thecoverage percentage reaches 0% at a certain distance from the edge ofthe brightness enhancement film. As shown in FIG. 23 , the center of thebrightness enhancement film includes no yellow ink. The shape of profile148 may match the shape of profile 144 in FIG. 18 to ensure a uniformdisplay color from the center of the display to the edge of the display.The shape of the profile shown in FIG. 23 is merely illustrative. Ingeneral, the profile may have any desired shape.

In addition to mitigating edge color non-uniformity, the yellow ink onthe brightness enhancement film has the added benefit of decreasing thecoefficient of friction (COF) of the brightness enhancement film. Ingeneral, it may be desirable for the brightness enhancement film(s) tohave a low coefficient of friction to prevent the film fromwrinkling/buckling during operation of the display. As an example,normal operation of the display may result in the brightness enhancementfilms undergoing temperature changes that cause expansion andcontraction of the film. In these scenarios, it is desirable for thebrightness enhancement film not to buckle.

The presence of ink dots on the lower surface of substrate 114-1decreases the coefficient of friction for the lower surface of substrate114-1. This effect may be leveraged for friction improvements even ifcolor compensation is not desired or required in the display. Forexample, clear ink dots may be uniformly distributed across the lowersurface of brightness enhancement film 44-1. FIG. 24 is across-sectional side view of an illustrative brightness enhancement film44-1 with clear ink dots 150 evenly distributed across lower surface114-B of substrate 114-1.

FIG. 25 is a graph of the clear ink coverage percentage as a function ofposition across the brightness enhancement film. As shown by profile152, the clear ink coverage percentage (e.g., the total percentage ofunit area of surface 114-B that is covered with clear ink) remainsconstant from the edge of the brightness enhancement film to the centerof the brightness enhancement film. This profile is merely illustrative.If desired, clear ink dots may be distributed in a varying manner (e.g.,with increasing density in the edges of the film as in FIG. 23 ) oraccording to any other desired profile.

As yet another example, both yellow ink dots and clear ink dots may beprinted on a single brightness enhancement film (for both the opticalcompensation described in connection with FIGS. 20-23 and maximizing thefriction improvements described in connection with FIGS. 24 and 25 ).FIG. 26 is a graph of showing the coverage percentage of yellow andclear ink across the display. As shown, at the edge of the brightnessenhancement film, there may be no clear ink (e.g., a coverage percentageof 0%) and the yellow ink coverage percentage may be at a magnitude P₁.At the center of the brightness enhancement film, there may be no yellowink (e.g., a coverage percentage of 0%) and the clear ink coveragepercentage may be at a magnitude P₁. The clear ink and yellow inkcoverage percentage profiles may mirror each other such that the totalink coverage percentage remains constant cross the brightnessenhancement film. In other words, the coverage percentage of yellow inkdecreases with increasing distance from the edge of the brightnessenhancement film whereas the coverage percentage of clear ink increaseswith increasing distance from the edge of the brightness enhancementfilm. The slopes of the profiles for the yellow and clear ink thereforemay have the same magnitude but different signs at each position. Theshapes of the profiles shown in FIG. 26 are merely illustrative. Ingeneral, the profiles may have any desired shapes.

The aforementioned examples of applying clear and/or yellow ink to thebottom surface of substrate 114-1 for brightness enhancement film 44-1are merely illustrative. In general, yellow ink for optical compensation(or yellow ink and clear ink as described in connection with FIG. 26 )may be applied to any surface of any optical film that is positionedabove phosphor layer 40 in the backlight (e.g., as shown in FIG. 4 ).For example, yellow ink may be applied to film 108 in color conversionlayer 34, brightness enhancement film 44-1, or brightness enhancementfilm 44-2. The yellow ink may be applied to the lower surface of anoptical film or the upper surface of an optical film. Yellow ink may beapplied to multiple optical films in the backlight unit (e.g.,brightness enhancement film 44-1 and brightness enhancement film 44-2)if desired.

In general, clear ink for friction improvements may be applied to anysurface of any optical film in the backlight (e.g., as shown in FIG. 4). For example, clear ink may be applied to one of light spreadinglayers 28-1, 28-2, and 28-3, color conversion layer 34, brightnessenhancement film 44-1, or brightness enhancement film 44-2. The clearink may be applied to the lower surface of an optical film or the uppersurface of an optical film. Clear ink may be applied to multiple opticalfilms in the backlight unit (e.g., brightness enhancement film 44-1 andbrightness enhancement film 44-2) if desired.

As an example, yellow ink may be applied according to the gradient ofFIG. 23 to the edges of the bottom surface of substrate 114-1 ofbrightness enhancement film 44-1 while clear ink may be applieduniformly across the bottom surface of substrate 114-2 of brightnessenhancement film 44-2.

FIG. 27 is a top view of an illustrative LED array with LEDs 38 formedacross printed circuit board 50. This arrangement may be used in any ofthe backlight units described herein (e.g., the backlight of FIG. 4 ,the backlight of FIG. 11 , etc.). As shown, LEDs 38 may be distributedacross an active area (AA) of the display. The active area is thefootprint of the display that actually emits light, and may be definedby an opaque masking layer in the display stack-up. Herein, the display,printed circuit board, backlight unit, optical films, and other desireddisplay layers may all be referred to as having an active area. Theactive area of each layer may simply refer to the footprint of eachlayer that overlaps with the light-emitting area of the display. In theexample of FIG. 27 , the active area has rounded corners. This exampleis merely illustrative. In general, the active area may have any desiredshape. Printed circuit board 50 may have an inactive area (e.g., an areathat does not vertically overlap the light-emitting footprint of thedisplay) in addition to the active area.

In addition to LEDs being mounted on printed circuit board 50,additional electronic components 154 (sometimes referred to as surfacemount components) may be mounted to printed circuit board 50. Theprinted circuit board may have an edge 50E in the inactive area thatincludes components 154. Components 154 may include, for example,driving circuitry (e.g., one or more display driver integrated circuits)that is used to control LEDs 38 in the LED array. Components 154 may beattached to the upper surface of the printed circuit board using solder.As shown in FIG. 27 , the components 154 are consolidated in one edge50E of the printed circuit board. This allows only one edge of theprinted circuit board to have a larger gap between the edge of theprinted circuit board and the active area (e.g., distance 156 in FIG. 27). The remaining three edges of the printed circuit board have a smallergap between the edge of the printed circuit board and the active area(e.g., distance 158 in FIG. 27 ).

To increase the efficiency of the backlight unit and display, it may bedesirable for printed circuit board 50 to be as reflective as possible.To increase the reflectivity of printed circuit board 50, one or morelayers in the printed circuit board may be formed from highly reflectivematerials. FIG. 28 is a cross-sectional side view of a highly reflectiveprinted circuit board 50 that may be used in any of the backlight unitsdescribed herein (e.g., the backlight of FIG. 4 , the backlight of FIG.11 , etc.).

As shown in FIG. 28 , printed circuit board 50 includes first, second,and third conductive layers 162-1, 162-2, and 162-3. These conductivelayers may be patterned to form the desired conductive routing withinthe printed circuit board. The conductive layers may be formed fromcopper or another desired conductive material.

A solder resist layer 160-1 is formed on the upper surface of conductivelayer 162-1. Solder resist layer 160-1 forms the top-most layer of theprinted circuit board and therefore may be a key driver of thereflectivity of the printed circuit board. Accordingly, solder resistlayer 160-1 may be formed from a white dielectric material that reflectsthe majority of incident light (e.g., a reflectivity greater than 60%,greater than 80%, greater than 90%, greater than 95%, greater than 98%,etc.).

Electronic components such as LED 38 may be mounted to conductive layer162-1 using solder 172. In general, any desired components may bemounted on the upper surface of printed circuit board 50 in respectiveopenings in solder resist layer 160-1.

Between conductive layers 162-1 and 162-2, a white core layer 164 isformed. In areas where solder resist layer 160-1 is removed to allowelectronic components to be mounted, the white core layer 164 may beexposed as the upper-most surface of the printed circuit board. Thewhite core may therefore also have a high reflectivity (e.g., areflectivity greater than 60%, greater than 80%, greater than 90%,greater than 95%, greater than 98%, etc.) to increase the reflectivityof the printed circuit board. The white core may be thicker than theremaining layers (160-1, 162-1, 162-2, 166, 162-3, 160-2, 168, and 170)in the printed circuit board. The white core may be formed form adielectric material that insulates conductive layer 162-1 fromconductive layer 162-2.

Between conductive layers 162-2 and 162-3, a prepreg layer 166 (e.g., adielectric layer that insulates conductive layer 162-2 from conductivelayer 162-3) is formed. An additional solder resist layer 160-2 isformed beneath conductive layer 162-3. Solder resist layer 160-2 may beformed from a white dielectric material that reflects the majority ofincident light (e.g., a reflectivity greater than 60%, greater than 80%,greater than 90%, greater than 95%, greater than 98%, etc.).

The dielectric constants of layers 160-1, 164, 166, and 160-2 may beselected to help mitigate parasitic capacitance. As one example, thedielectric constant for prepreg layer 166 may be lower than thedielectric constant for solder resist layer 160-2, the dielectricconstant for solder resist layer 160-2 may be lower than the dielectricconstant for white core layer 164, and the dielectric constant for whitecore layer 164 may be lower than the dielectric constant for solderresist layer 160-1. The thickness of solder resist layer 160-2 may belower than the thickness of solder resist layer 160-1, the thickness ofsolder resist layer 160-1 may be lower than the thickness of prepreglayer 166, and the thickness of prepreg layer 166 may be lower than thethickness of white core layer 164. This type of arrangement may providethe printed circuit board with optimized reflectance and parasiticcapacitance.

A conductive shield 170 may be attached to the lower surface of solderresist layer 160-2 using adhesive layer 168. Conductive shield 170 maybe formed from copper or any other desired conductive material. Adhesivelayer 168 and conductive shield 170 may be considered part of theprinted circuit board or may be considered to be attached to a lowersurface of the printed circuit board.

In one arrangement, shown in FIG. 29 , each LED may be mounted toprinted circuit board 50 in a respective circular opening 174 in solderresist layer 160-1. Solder 172 may attach the LED to the conductivelayers (e.g., conductive layer 162-1) of printed circuit board 50 thatare exposed within opening 174 (sometimes referred to as solder resistopening 174). In FIG. 29 , opening 174 is a circular opening having adiameter 176. However, the reflectance of the printed circuit board maybe slightly lower in the opening area than in the areas covered bysolder resist layer 160-1. To increase reflectivity of the printedcircuit board (and, accordingly, efficiency of the display), the printedcircuit board may instead include rectangular solder resist openings 174as shown in FIG. 30 .

Rectangular openings 174 in FIG. 30 have a width 178 and height 180.Both width 178 and height 180 may be lower than diameter 176 in FIG. 29. As one example, width 178 may be less than 500 microns, less than 400microns, between 300 and 400 microns, or any other desired distance.Height 180 may be less than 600 microns, less than 500 microns, between400 and 500 microns, or any other desired distance. In one example, thecircular opening in FIG. 29 has a diameter of 500 microns and therectangular opening of FIG. 30 is 350 microns by 450 microns. Therectangular opening is approximately 80% of the total size of thecircular opening in this example. This reduced opening size increasesthe reflectance of the printed circuit board which in turn increases theefficiency of the display.

The shape and dimensions of the solder resist openings in FIGS. 29 and30 are merely illustrative. In general, a solder resist opening of anydesired shape (e.g., square, non-square rectangular, circular, etc.) anddimensions may be used.

FIG. 31 is a top view of printed circuit board 50 showing how the solderresist layer 160-1 may be selectively extended towards the edge of theprinted circuit board to prevent delamination. As shown in FIG. 31 ,solder resist layer 160-1 may, in general be separated from the edge ofprinted circuit board 50 by distance 182. However, in some locations,there may be tightly spaced components close to the edge of the printedcircuit board that require tightly spaced solder resist openings 174close to the edge of the printed circuit board. Due to the small surfacearea of the remaining solder resist layer between the solder resistopenings, there is a risk of delamination of the solder resist layerduring operation of the display if the same solder-resist-to-edge gap182 was maintained in this region.

To prevent delamination, the solder resist layer may have a locallyprotruding portion 188 (sometimes referred to as tab 188) that extendscloser to the edge of the printed circuit board. As shown in FIG. 31 ,tab 188 is separated from the edge of printed circuit board by distance184 that is less than distance 182. This results in the solder resistlayer having a width 186 between openings 174 and the edge of the solderresist layer. This increased width 186 (relative to if the tab was notincluded) reduces the chances of delamination during operation.

Distance 184 may be less than 300 microns, less than 200 microns, lessthan 150 microns, less than 120 microns, more than 100 microns, morethan 50 microns, between 50 and 150 microns, between 100 and 110microns, or any other desired distance. Distance 186 may be less than300 microns, less than 200 microns, less than 150 microns, more than 100microns, more than 120 microns, more than 140 microns, between 125 and175 microns, between 140 and 150 microns, or any other desired distance.Distance 182 may be less than 300 microns, less than 200 microns, lessthan 150 microns, more than 100 microns, more than 50 microns, between125 and 175 microns, between 140 and 160 microns, or any other desireddistance.

FIG. 32 is a cross-sectional side view of an illustrative light-emittingdiode. As shown, each light-emitting diode 38 may be formed as alight-emitting diode package that is attached to the underlying printedcircuit board using solder 172. The light-emitting diode package 38 hasa package substrate 192 and LED layers 194 formed on the packagesubstrate. LED substrate 192 may be formed from sapphire, galliumnitride (GaN), gallium arsenic (GaAs), silicon, or any other desiredsemiconductor and dielectric materials. Substrate 192 may be patternedto include protrusions as shown in FIG. 32 . LED layers 194 may includeone or more n-type semiconductor layer(s) and/or one or more p-typesemiconductor layers on LED substrate 192. The n-type semiconductorlayer(s) may include materials such as n-type doped gallium nitride(GaN), n-type aluminum gallium indium phosphide (AlGaInP), etc. Then-type semiconductor layer(s) may be an epitaxial layer (e.g., formedusing epitaxy-type crystal growth / material deposition). The p-typesemiconductor layer(s) may include p-type doped gallium nitride (GaN) orany other desired material. The p-type semiconductor layer(s) may be anepitaxial layer (e.g., formed using epitaxy-type crystal growth /material deposition). The LED layers may conform to the patternedsurface of substrate 192.

The LED package may also include one or more passivation layers toprevent solder overflow from electrically connecting (shorting) to theLED layers 194 in the package. As shown in FIG. 32 , the LED includes afirst passivation layer 196-1 (sometimes referred to as dielectric layer196-1, coating 196-1, etc.) and a second passivation layer 196-2(sometimes referred to as dielectric layer 196-2, coating 196-2, etc.).

The first passivation layer 196-1 directly contacts the substrate 192and conforms to the protrusions of the patterned surface of substrate192. The passivation layer 196-1 may be formed from any desired material(e.g., aluminum oxide (Al₂O₃) or another desired material). Thepassivation layer 196-1 may be applied using atomic layer deposition(ALD) to ensure there are no voids in the areas between the protrusionsof the patterned surface of substrate 192. Passivation layer 196-1 maytherefore sometimes be referred to as an ALD aluminum oxide layer. Thepassivation layer 196-2 may be formed from any desired material (e.g.,silicon dioxide (SiO₂) or another desired material). The passivationlayer 196-2 may be applied using plasma-enhanced chemical vapordeposition (PECVD). Passivation layer 196-2 may therefore sometimes bereferred to as an PECVD silicon dioxide layer.

Passivation layer 196-1 is interposed between (and in direct contactwith) substrate 192 and passivation layer 196-2 at the edge of thepackage. Passivation layer 196-1 is interposed between (and in directcontact with) LED layers 194 and passivation layer 196-2 in a centralportion of the package. Passivation layer 196-2 may be adjacent toadditional dielectric and/or reflective layers. For example, passivationlayer 196-2 may be adjacent to a physical vapor deposition (PVD)SiO₂/TiO₂ coating.

As previously shown in FIG. 27 , additional electronic components 154(sometimes referred to as surface mount components) may be mounted to anedge of printed circuit board 50. During a drop event, one or moreoptical films 26 in the backlight unit may shift into the edge of theprinted circuit board with the electronic components 154. If care is nottaken, one of the optical films may strike an electronic component 154and dislodge the component from the printed circuit board. To ensure thereliability of components 154, mechanical structures may be included inthe edge of the printed circuit board to prevent the components frombeing dislodged during a drop event.

FIG. 33 is a top view of a display that includes mechanical structuresto protect electronic components in the edge of the display. As shown inFIG. 33 , a plurality of electronic components 154 are attached to theedge portion 50E of printed circuit board 50. Each electronic component154 may be electrically and mechanically connected to the printedcircuit board using solder, as an example.

To protect electronic components 154, standoffs such as standoff 198 andstandoff 200 may also be attached to the edge of the printed circuitboard. The standoffs may sometimes be referred to as spacer structures,protection structures, standoff structures, buffer structures, bumperstructures, etc. Standoff 198 may be a surface-mount technology (SMT)component that is attached to the printed circuit board using solder,whereas standoff 200 may be attached to the printed circuit board usingadhesive. The standoffs are intended to absorb any potential impact fromoptical films 26 during a drop event and are therefore positioned closerto the active area AA than the active electronic components 154. Asshown in FIG. 33 , the distance 202 between the electronic components154 (e.g., the closest electronic component to the border) and theborder of the active area is greater than distances 204/206 between thestandoffs and the border of the active area.

The printed circuit board may have available area where a conductivelayer of the printed circuit board (e.g., copper layer 162-1 in FIG. 28) is not used for other routing/mounting and therefore may be availablefor mechanically securing the standoffs. Standoff 198 may be attached toavailable portions of conductive layer 162-1 using solder. Even whenstandoff 198 is attached to the printed circuit board using solder inthis manner, the standoff serves only a mechanical function and does notserve any electrical function within the device. The standoff is simplymeant to absorb any potential impact from optical films 26 during a dropevent. The conductive portion of the printed circuit board to whichstandoff 198 is soldered may not be used to convey signals for theelectronic device (e.g., a floating portion that is only used forattachment purposes).

Standoff 198 and electronic components 154 may both be attached to theprinted circuit board using surface-mount technology (SMT). This mayallow standoff 198 and electronic components 154 to be attached to theprinted circuit board in the same manufacturing step (e.g., a singlereflow) if desired.

Although forming the standoffs as SMT components may sometimes beconvenient from a manufacturing perspective, there may be portions ofthe printed circuit board that have otherwise empty spaces (that arecandidates for a standoff structure) but do not have availableconductive layer for an SMT attachment. Standoffs 200 in these areas maytherefore be attached using adhesive. Standoffs 200 may be attached toan upper surface of the printed circuit board such as solder-resistlayer 160-1 (see FIG. 28 ) using adhesive. In general, any type ofadhesive may be used (e.g., pressure sensitive adhesive, ultravioletlight curable (UV-curable) adhesive, etc.). Standoff 200 serves only amechanical function and does not serve any electrical function withinthe device. The standoff is simply meant to absorb any potential impactfrom optical films 26 during a drop event.

Any desired number of standoffs 198 be attached to the edge 50E of theprinted circuit board using solder (e.g., one standoff, two standoffs,more than two standoffs, more than three standoffs, more than fivestandoffs, more than ten standoffs, more than twenty standoffs, etc.).Any desired number of standoffs 200 be attached to the edge 50E of theprinted circuit board using adhesive (e.g., one standoff, two standoffs,more than two standoffs, more than three standoffs, more than fivestandoffs, more than ten standoffs, more than twenty standoffs, etc.).

FIG. 34 is a top view of printed circuit board 50 showing how certaincomponents may have additional encapsulant to further protect thecomponents during a drop event. FIG. 34 shows electronic components154-1, 154-2, 154-3, and 154-4 mounted to edge 50E of printed circuitboard 50. As one example, electronic component 154-1 may be a driverintegrated circuit used to control LEDs 38 in the active area AA.Electronic components 154-2, 154-3, and 154-4 may include one or more ofa capacitor, a resistor, an inductor, or any other desired component.

Electronic components 154-2, 154-3, and 154-4 may be at a high risk forbeing dislodged during a drop event. Accordingly, encapsulant may beformed around the components to provide additional physical protectionfor the components. Encapsulant 208-1 is formed around electroniccomponent 154-2, encapsulant 208-2 is formed around electronic component154-3, and encapsulant 208-3 is formed around electronic component154-4.

As shown in FIG. 34 , each encapsulant portion may surround a respectiveelectronic component on three sides, with the side of the electroniccomponent adjacent/closest to electronic component 154-1 being leftopen. Using the three-sided encapsulant as in FIG. 34 may prevent theencapsulant from undesirably contacting component 154-1 (which may causeadditional reliability issues). Therefore, encapsulant 208-1 is formedon three sides of component 154-2 but is not interposed betweencomponents 154-2 and 154-1 (e.g., is not formed on the fourth side ofcomponent 154-2). Encapsulant 208-2 is formed on three sides ofcomponent 154-3 but is not interposed between components 154-3 and154-1(e.g., is not formed on the fourth side of component 154-3).Encapsulant 208-3 is formed on three sides of component 154-4 but is notinterposed between components 154-4 and 154-1(e.g., is not formed on thefourth side of component 154-4).

As shown in FIG. 28 , the printed circuit board may include a shieldinglayer that is electrically connected to ground. This shielding layer maytherefore ground the printed circuit board and provide shielding for theprinted circuit board. The shielding layer may be electrically connectedto an exposed portion of conductive layer 162-3 within the printedcircuit board. FIG. 35 is a top view of a rear surface (i.e., a rearview) of the printed circuit board 50 showing how conductive layer 162-3is exposed at the edges of the printed circuit board. Solder resistlayer 160-2 may cover the majority of the footprint of the printedcircuit board. However, solder resist layer 160-2 is removed along threeof the four edges of the printed circuit board to expose conductivelayer 162-3, as shown in FIG. 35 .

The conductive layer 162-3 may be exposed (and electrically connected toa shielding layer) along three edges of the printed circuit board.However, the conductive layer 162-3 is not exposed (or electricallyconnected to a shielding layer) along edge 50E that includes electroniccomponents 154 in an inactive area (as shown in FIG. 27 , for example).This may prevent interference with the electronic components in theinactive area of edge 50E.

FIG. 36 is a cross-sectional side view of an illustrative displayshowing how the exposed conductive layer in the printed circuit board iselectrically connected to a shielding layer. As shown in FIG. 36 ,solder resist layer 160-2 of printed circuit board 50 is removed alongan edge of the printed circuit board to expose conductive layer 162-3.The conductive layer 162-3 in this exposed area may be electricallyconnected to shielding layer 170 by conductive adhesive layer 210.Conductive adhesive layer 210 is therefore formed along three edges ofthe printed circuit board (e.g., following the C-shaped footprint ofFIG. 35 ). Conductive adhesive layer 210 may be a conductive pressuresensitive adhesive or any other desired type of conductive adhesive.

Adhesive layer 210 mechanically and electrically connects conductivelayer 162-3 to shielding layer 170. An additional adhesive layer 168(e.g., a dielectric adhesive layer) may be interposed between solderresist-layer 160-2 and shielding layer 170. In other words, a conductiveadhesive layer attaches the shielding layer to the printed circuit boardin areas of the printed circuit board where conductive material isexposed on a lower surface and a dielectric adhesive layer attaches theshielding layer to the printed circuit board in areas of the printedcircuit board where insulating material is exposed.

Adhesive layer 168, adhesive layer 210, and conductive shield 170 may beconsidered part of the printed circuit board 50 or may be considered tobe attached to a lower surface of the printed circuit board 50.

Additional adhesive layer 168 may extend across the entire footprint ofthe printed circuit board. In other words, the adhesive layer 168 mayattach the shielding layer 170 in all the regions of the printed circuitboard where conductive layer 162-3 is not exposed (and solder resistlayer 160-2 is therefore exposed). Adhesive layer 210 may attach theshielding layer 170 in all the regions of the printed circuit boardwhere conductive layer 162-3 is exposed. Adhesive layer 168 is notconductive and may be referred to as a dielectric adhesive layer.Adhesive layer 168 may be a pressure sensitive adhesive or any otherdesired type of adhesive.

Adhesive layer 168 may have a low dielectric constant to reducecapacitance and thereby save power. For example, adhesive layer 168 mayhave a dielectric constant that is less than 4, less than 3, less than2.5, between 2 and 3, or any other desired dielectric constant. Adhesivelayer 168 may also have a low water permeability to prevent water fromreaching printed circuit board 50 and causing issues such as browning.Adhesive layer 168 may have a water vapor transmission rate (WVTR)(measured at 40° C. and 100% relative humidity in units of g/m²/day) ofless than 200, less than 100, less than 75, less than 50, more than 25,between 25 and 75, between 40 and 50, or any other desired magnitude.

A layer of black ink 212 may optionally be formed on the shielding layer170. Shielding layer 170 in FIG. 36 may be formed from copper and maytherefore sometimes be referred to as copper foil 170. Copper foil 170may have a thickness of less than 20 microns, less than 15 microns, lessthan 10 microns, more than 5 microns, between 5 and 20 microns, between5 and 15 microns, or any other desired thickness.

FIG. 36 also shows how a chassis 214 may be formed on the printedcircuit board 50. Chassis 214 may be a plastic chassis (sometimesreferred to as a p-chassis) that supports other layers (e.g., layers inbacklight structures 42 and/or pixel array 24) in the display. Chassis214 may extend around the periphery of printed circuit board with acentral opening in which the LED array is formed (e.g., chassis 214 maybe ring-shaped). In one possible arrangement, chassis 214 may have aC-shaped footprint similar to the footprint of exposed conductive layer162-3 and conductive adhesive layer 210 (as shown in FIG. 35 ). In otherwords, the chassis extends along three edges of the printed circuitboard but does not extend along edge 50E of the printed circuit board.

Chassis 214 may be attached to printed circuit board using adhesivelayer 216. One or more layers within the electronic device (such aspixel array 24) may be attached to chassis 214 (e.g., the upper surfaceof the chassis) using an adhesive layer such as adhesive layer 218. Anydesired type of adhesive (e.g., pressure sensitive adhesive) may be usedfor adhesive layers 216 and 218.

As shown in FIG. 36 , a conductive tape layer 220 may be attached to thelower surface of copper foil 170, wrap around p-chassis 214 (contactingthe side surface of p-chassis 214), and attach to pixel array 24.Conductive tape 220 may electrically connect portions of pixel array 24to ground. Conductive tape 220 may include indium tin oxide (ITO) andmay be referred to as ITO tape 220. Conductive tape 220 may include anyother desired material(s).

To summarize, the exposed portion of conductive layer 162-3 in printedcircuit board 50, conductive adhesive layer 210, shielding layer 170,and conductive tape 220 may all form part of the grounding structuresfor backlight unit 42 and/or pixel array 24. The grounding structuresmay also be used to electrically shield the backlight unit and/or thepixel array. One or more of these grounding components may beelectrically connected to other grounding structures within the device(e.g., a conductive housing structure).

FIG. 37 is a cross-sectional side view of a backlight unit in a displayshowing how an optical film may be attached to a shelf in the p-chassis.As previously mentioned, it is desirable to prevent damage to electroniccomponents 154 in edge 50E of printed circuit board (in the inactivearea of the display) in a drop event. To help prevent the optical filmsin the backlight unit from shifting during a drop event, one of theoptical films may be attached to a shelf in the p-chassis.

As shown in FIG. 37 , chassis 214 has a top surface 214-T and a bottomsurface 214-B. Chassis 214 also has a protruding portion 222 that formsa shelf surface 214-S. Surface 214-S may be parallel (e.g., planeparallel) to surface 214-T, surface 214-B and the XY-plane in FIG. 37 .Surface 214-S is interposed between surfaces 214-B and 214-T.

One of the optical films 26 in the backlight unit is mounted on shelfsurface 214-S. In the example of FIG. 37 , the backlight unit hasoptical films having the arrangement of FIG. 4 , with three lightspreading layers, a color conversion layer 34, and first and secondbrightness enhancement films 44-1 and 44-2. In this example, colorconversion layer 34 is attached to shelf surface 214-S of chassisprotrusion 222 using adhesive layer 224. Color conversion layer 34 maybe the thickest layer of the optical films 26. Color conversion layer 34may therefore have the most momentum during a drop event and may themost susceptible optical film to shift and damage components in edge 50Eof the printed circuit board. Therefore, color conversion layer 34 (thethickest layer) may be selected as the optical film to be attacheddirectly to chassis 214. This example is merely illustrative. Ingeneral, any one of the optical films 26 may be directly attached tochassis 214 using adhesive.

An adhesive layer 226 may also attach chassis 214 to the upper surfaceof printed circuit board 50. Any desired type of adhesive (e.g.,pressure sensitive adhesive) may be used for adhesive layers 224 and226. Adhesive layer 226 may optionally be formed integrally withadhesive layer 216 shown in FIG. 36 .

Only one edge of the p-chassis 214 may have protrusion 222 to provide ashelf for one of the optical films. FIG. 38 is a top view of chassis214. As shown, the p-chassis extends along three sides of the printedcircuit board and is omitted along the edge 50E of the printed circuitboard with electronic components 154. Along the top edge and bottom edgeof the printed circuit board, the chassis may have an arrangement of thetype shown in FIG. 36 (without protrusion 222). Along the right edge ofthe printed circuit board (e.g., the edge opposing edge 50E), chassis214 includes protrusion 222 to form a shelf for the optical filmattachment (e.g., the chassis has the arrangement shown in FIG. 37 ).Forming the shelf opposite edge 50E helps prevent the optical films fromshifting in the negative X-direction towards edge 50E and components 154during a drop event.

The width of adhesive 228 between chassis protrusion 222 and colorconversion film 34 may be greater than 0.2 millimeters, greater than 0.4millimeters, greater than 0.6 millimeters, greater than 1.0 millimeters,less than 1.5 millimeters, between 0.5 and 1 millimeters, or any otherdesired distance. The adhesive 228 may extend along the entire rightedge of the printed circuit board (e.g., from the upper edge to thelower edge). In other words, the length of adhesive 228 may be more than80% of the length of the printed circuit board, more than 90% of thelength of the printed circuit board, more than 95% of the length of theprinted circuit board, etc.

FIG. 39 is a cross-sectional side view of display 14 showing how one ormore metal stiffeners may be incorporated into the display. FIG. 39shows edge 50E of printed circuit board 50 with corresponding electroniccomponents 154. Optical films 26 are mounted over printed circuit board50 in the active area of the display.

The electronic device may also include a printed circuit board 230underneath printed circuit board 50 (with LEDs for the backlight unit).Printed circuit board 230 may be used for electrical components withinthe electronic device and sometimes may be referred to as a main boardor motherboard. A flexible printed circuit board 234 may be electricallyconnected between printed circuit board 230 and pixel array 24. Theflexible printed circuit board 234 wraps around the edge 50E of printedcircuit board 50. A timing controller 238 (e.g., an integrated circuit)that is used to control pixel array 24 may be mounted on flexibleprinted circuit 234. To provide additional structural integrity to theflexible printed circuit board in an area overlapping timing controller238, a stiffener 236 is attached to the lower surface of flexibleprinted circuit 234 underneath timing controller 238. Stiffener 236 maybe formed from stainless steel or another desired material.

To protect electronic components 154 in edge 50E and provide the displaywith additional structural integrity, a stiffener 232 may be interposedbetween printed circuit board 50 and printed circuit board 230.Stiffener 232 may wrap around the edge 50E of printed circuit board. Thestiffener 232 has an upper portion 232-U that is formed over and isvertically overlapping with components 154 in edge 50E, a lower portion232-L that is formed underneath and is vertically overlapping withcomponents 154 in edge 50E, and an edge portion 232-E that extendsvertically to connect the upper portion 232-U and the lower portion232-L. Upper portion 232-U is also attached to and provides mechanicalsupport (e.g., at least partially supports) pixel array 24.

To help decouple stress between printed circuit board 50 and printedcircuit board 230 / flexible printed circuit 234 / timing controller238, stiffener 232 may extend along the entire interface between printedcircuit boards 50 and 230. The footprint of stiffener 232 may at leastmatch the footprint of printed circuit board 230. Said another way, allor most of the footprint of printed circuit board 230 (e.g., greaterthan 80% of the footprint, greater than 90% of the footprint, greaterthan 95% of the footprint, greater than 99% of the footprint, etc.) maybe vertically overlapped by stiffener 232. This reduces the stressapplied to printed circuit board 50. Stiffener 232 may be formed fromstainless steel or another desired material. The footprint of stiffener232 may also at least match the footprint of printed circuit board 50.Said another way, all or most of the footprint of printed circuit board50 (e.g., greater than 80% of the footprint, greater than 90% of thefootprint, greater than 95% of the footprint, greater than 99% of thefootprint, etc.) may be vertically overlapped by stiffener 232.

In some displays (e.g., as shown in FIG. 3 ), the light-emitting diodesfor the display may be arranged in a grid. The light-emitting diodes maybe arranged in evenly spaced rows and columns that extend along theentire display. This type of arrangement may be referred to as a squaregrid or a rectangular grid. However, having the light-emitting diodesarranged in a rectangular grid may result in visible artifacts(sometimes referred to as grid mura) when operating the display. Tomitigate visible artifacts associated with the positioning of thelight-emitting diodes in a grid, the positions of the light-emittingdiodes may be dithered. In other words, the actual position of eachlight-emitting diode may be adjusted relative to the rectangular-gridposition for that light-emitting diode.

FIG. 40 is a diagram showing how the positions of light-emitting diodesmay be dithered to improve performance of the display. FIG. 40 showsrectangular grid positions 302-1, 302-2, 302-3, and 302-4. Therectangular grid positions may be positions associated with a regularlyspaced grid that extends across the entire display (e.g., eachrectangular grid position is part of a row of rectangular grid positionsthat extends across the entire display and each rectangular gridposition is part of a column of rectangular grid positions that extendsacross the entire display). Light-emitting diodes may optionally bemounted at each rectangular grid position (similar to as in FIG. 3 ).Alternatively, to mitigate visible artifacts caused by this arrangementthe light-emitting diodes may be offset from the rectangular gridpositions as shown in FIG. 40 .

In FIG. 40 , each light-emitting diode may be positioned at a positionthat is offset relative to its corresponding rectangular grid position.For example, a light-emitting diode may be located at position 306-1that is moved by offset distance 304-1 away from rectangular gridposition 302-1. Offset distance 304-1 is at an angle 308-1 relative tothe X-axis. Similarly, a light-emitting diode may be located at position306-2 that is moved by offset distance 304-2 away from rectangular gridposition 302-2. Offset distance 304-2 is at an angle 308-2 relative tothe X-axis. A light-emitting diode may be located at position 306-3 thatis moved by offset distance 304-3 away from rectangular grid position302-3. Offset distance 304-3 is at an angle 308-3 relative to theX-axis. A light-emitting diode may be located at position 306-4 that ismoved by offset distance 304-4 away from rectangular grid position302-4. Offset distance 304-4 is at an angle 308-4 relative to theX-axis.

Each offset distance may have any desired magnitude. In one example, theoffset distance may be greater than 0, may be shorter than a distancebetween adjacent rectangular grid positions in the same row (e.g.,distance 307), and may be shorter than a distance between adjacentrectangular grid positions in the same column (e.g., distance 309). Eachoffset distance may be the same (e.g., offset distances 304-1, 304-2,304-3, and 304-4 may all have the same magnitude) or one or more of theoffset distances may be different (e.g., offset distances 304-1, 304-2,304-3, and 304-4 may all have different magnitudes). In some cases, theoffset distances may be random or pseudo-random.

Similarly, each offset distance may be moved away from its correspondingrectangular grid position by any desired angle. In one illustrativeexample, each angle is 90 degrees offset from the angle associated withthe light-emitting diode in an adjacent row or column. As shown in FIG.40 , angle 304-4 may be a given angle (e.g., 0) between 0 degrees and 90degrees, angle 304-2 may be offset by 90 degrees relative to the givenangle (e.g., angle 304-2 = θ + 90 degrees), angle 304-1 may be offset by180 degrees relative to the given angle (e.g., angle 304-1 = θ + 180degrees), and angle 304-3 may be offset by 270 degrees relative to thegiven angle (e.g., angle 304-3 = θ + 270 degrees). Effectively, the 2x2group of light-emitting diodes is rotated relative to the rectangulargrid positions. Each 2x2 group of light-emitting diodes within thedisplay may be independently rotated. The example of using a 2x2 groupis merely illustrative. Light-emitting diode groups of any desired sizemay be rotated across the display.

Each light-emitting diode position 306 may be offset from itsrectangular grid position 302 by an angle that is 180 degrees differentthan the light-emitting diode position of a diagonally adjacentlight-emitting diode. Each light-emitting diode position 306 may beoffset from its rectangular grid position 302 by an angle that is 90degrees different than the light-emitting diode position of ahorizontally adjacent light-emitting diode (e.g., a light-emitting diodein the same row). Each light-emitting diode position 306 may be offsetfrom its rectangular grid position 302 by an angle that is 90 degreesdifferent than the light-emitting diode position of a verticallyadjacent light-emitting diode (e.g., a light-emitting diode in the samecolumn).

This example is merely illustrative. In general, the location of eachlight-emitting diode and the rectangular grid position associated withthat light-emitting diode may be offset by any desired angle. In somecases, the angles may be random or pseudo-random. It should be notedthat each aforementioned light-emitting diode position may be theposition of one light-emitting diode or multiple light-emitting diodes(e.g., when multiple light-emitting diodes are used in each cell asdiscussed in connection with FIG. 3 ).

Additionally, it should be noted that, to prevent mura caused by thelight-emitting diodes 38, each light-emitting diode may emit lightwithin a narrow wavelength range. For example, every light-emittingdiode 38 in backlight unit 42 may emit light with a peak brightness at awavelength of within a 2 nanometer range, within a 1.5 nanometer range,within a 1.0 nanometer range, within a 0.8 nanometer range, within a0.75 nanometer range, within a 0.6 nanometer range, etc. Take theexample where the light-emitting diodes emit blue light. In thisexample, every light-emitting diode 38 in backlight unit 42 may emitlight with a peak brightness at a wavelength that is between (andincluding) 447.50 nanometers and 448.25 nanometers. In another example,every light-emitting diode 38 in backlight unit 42 may emit light with apeak brightness at a wavelength that is between (and including) 448.25nanometers and 449.00 nanometers. In general, any desired wavelengthrange may be used. However, the range may be narrow to mitigate muraartifacts.

FIG. 41 is a top view of an illustrative display with illustrativelight-emitting diodes that are positioned according to a dithered grid.As shown, each light-emitting diode 38 is dithered with respect to arectangular grid position (as shown in FIG. 40 ). In particular, each232 group of light-emitting diodes are rotated relative to theirrectangular grid positions. Therefore, the light-emitting diodes are notarranged in uniform rows and columns that extend across the entiredisplay. Dithering the location of the light-emitting diodes in this waymitigates grid mura associated with the light-emitting diodes in auniform rectangular grid. It should be noted that each light-emittingdiode position in FIG. 41 may be the position of one light-emittingdiode or multiple light-emitting diodes (e.g., when multiplelight-emitting diodes are used in each cell as discussed in connectionwith FIG. 3 ).

As shown in FIG. 41 , the active area AA may have an edge 310. If thesame LED layout pattern is used across the entire active area, therounded corner 312 may have a dimmer appearance than the remainingportions of the backlight. To mitigate non-uniformity in the roundedcorners of the active area, the pattern may be adjusted in the roundedcorners to increase the brightness in the rounded corners and match thebrightness of the rest of the backlight.

In the majority of the LED array (e.g., in the non-rounded-cornerareas), the LEDs may be separated by a pitch 314 in the X-direction anda pitch 316 in the Y-direction. Distances 314 and 316 may each be lessthan 100 millimeters, less than 10 millimeters, less than 5 millimeters,less than 4 millimeters, less than 3 millimeters, less than 2millimeters, greater than 1 millimeter, greater than 2 millimeters,between 2 and 3 millimeters, etc. Distance 316 may be slightly smallerthan distance 314 (e.g., less than 5% different, less than 1% different,etc.) in one possible arrangement. In general, any desired distances 314and 316 may be used.

In the rounded-corner areas, the LEDs may be separated by a pitch 318 inthe X-direction and a pitch 320 in the Y-direction. Pitch 318 in therounded corner area is less than pitch 314 in the non-rounded-cornerarea. Pitch 320 in the rounded corner area is less than pitch 316 in thenon-rounded-corner area. Pitch 318 may be less than pitch 314 by atleast 1%, at least 5%, at least 10%, at least 20%, at least 30%, atleast 40%, etc. Pitch 320 may be less than pitch 316 by at least 1%, atleast 5%, at least 10%, at least 20%, at least 30%, at least 40%, etc.Distances 318 and 320 may each be less than 100 millimeters, less than10 millimeters, less than 5 millimeters, less than 4 millimeters, lessthan 3 millimeters, less than 2 millimeters, less than 1.5 millimeters,less than 1 millimeter, greater than 1 millimeter, greater than 2millimeters, between 1.5 and 2.5 millimeters, between 1 and 1.5millimeters, etc.

The LEDs closest to the edge 310 of the active area (in both the roundedcorner areas and along the straight edges of the active area) may beseparated from edge 310 by less than 1 millimeter in the X-direction,less than 0.8 millimeters in the X-direction, less than 0.6 millimetersin the X-direction, etc. The LEDs closest to the edge 310 of the activearea (in both the rounded corner areas and along the straight edges ofthe active area) may be separated from edge 310 by less than 1millimeter in the Y-direction, less than 0.8 millimeters in theY-direction, less than 0.6 millimeters in the Y-direction, etc.

FIG. 42 is a cross-sectional side view of an illustrative display withreflective ink patterned on the encapsulant. As shown, LED 38 isattached to printed circuit 50 (e.g., an exposed portion of conductivelayer 162-1 as shown in FIG. 28 ) using solder 172. Encapsulant 52overlaps and conforms to the array of LEDs 38.

To mitigate hot-spots in the backlight unit, reflective ink 322 may bepatterned on top of the encapsulant 52. The reflective ink helps avoid abright spot directly over LEDs 38 in the backlight. A discrete portionof reflective ink 322 may overlap each LED 38 in the array of LEDs.Reflective ink 322 may be a white ink having a reflectivity that isgreater than 50%, greater than 70%, greater than 80%, greater than 90%,between 70% and 90%, between 70% and 95%, between 85% and 95%, etc. Thepatterned reflective ink may have any desired footprint when viewed fromabove (e.g., circular, non-square rectangular, square, etc.). Eachportion of patterned reflective ink 322 may have a diameter/width thatis greater than 300 microns, greater than 500 microns, greater than 600microns, greater than 800 microns, greater than 1000 microns, greaterthan 1300 microns, less than 1500 microns, less than 1300 microns, lessthan 1000 microns, less than 800 microns, less than 600 microns, between500 microns and 1500 microns, between 500 microns and 700 microns,between 900 microns and 1100 microns, etc. The center-to-centerdisplacement between each portion of reflective ink 322 and therespective light-emitting diode that ink portion overlaps may be lessthan 1000 microns, less than 750 microns, less than 600 microns, lessthan 500 microns, less than 400 microns, less than 300 microns, etc. Thetotal area of encapsulant 52 covered by reflective layer 322 (within theactive area) may be less than 15%, less than 10%, less than 5%, lessthan 3%, greater than 1%, between 1% and 15%, between 1% and 10%.

Optical films 26 may be formed over encapsulant 52 and reflective ink322. If desired, an optional support structure 324 may be included onprinted circuit board 50 between adjacent LEDs 38 within the LED array.Support structure 324 may be used to maintain the structural integrityof encapsulant slab 52 (which has a planar upper surface). Supportstructure 324 may have a low coefficient of thermal expansion (e.g.,lower than the encapsulant) to ensure it is not adversely affected bytemperature changes associated with operation of the light-emittingdiodes.

Support structure 324 may not affect the light emitted from thelight-emitting diodes. In other words, support structure 324 may beformed from a transparent material that has the same index-of-refractionas the surrounding encapsulant slab 52 (e.g., support structure 324 isindex-matched to slab 52). Support structure 324 will therefore notinfluence the path or intensity of the light emitted from light-emittingdiodes 38. Support structure 324 may therefore have any desired shape(since the shape will not affect the optical performance of thedisplay). In the example of FIG. 42 , support structure 324 has a curvedupper surface (e.g., a dome-shape).

As another alternative, support structure 324 may reflect light fromlight-emitting diodes 38. Support structure 324 may be formed from areflective material (e.g., a white structure, metal structure, etc.).Alternatively, support structure 324 may be formed from a transparentmaterial that has an index-of-refraction that is different than theindex-of-refraction of encapsulant layer 52. The index-of-refractiondifference may be sufficient (e.g., greater than 0.1, greater than 0.2,greater than 0.3, etc.) for total internal reflection (TIR) to occurwhen light from light-emitting diodes 38 reaches support structure 324.Support structure 324 may have a shape that is selected to redirectlight upwards towards the viewer.

When reflective ink 322 is included on the encapsulant, supportstructure 324 may be omitted from the backlight. Alternatively, supportstructure 324 may be index-matched to the encapsulant 52 so that thesupport structure provides mechanical strength but does not provideoptical functionality. As yet another alternative, a reflective supportstructure 324 may be included even when reflective ink 322 is includedon the encapsulant.

Including reflective ink 322 as in FIG. 42 may allow for one or moreoptical films 26 to be omitted from the backlight unit, mitigating thethickness, cost, and complexity of the backlight unit. For example, whenreflective ink 322 is used, instead of 6 optical films being includedbetween the LED array and the pixel array (e.g., as in FIG. 4 ), 5optical films, 4 optical films, or fewer than 4 optical films may beincluded between the LED array and the pixel array. As an example, twoof the three light spreading layers 28-1, 28-2, and 28-3 in FIG. 4 maybe omitted when reflective ink 322 is used.

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. A display, comprising: a printed circuit board;and an array of light sources mounted on the printed circuit board,wherein the printed circuit board comprises: a white core layer that hasa reflectivity of more than 80%; a first conductive layer on the whitecore layer; and a white solder resist layer on the first conductivelayer, wherein the white solder resist layer has a reflectivity of morethan 80%.
 2. The display defined in claim 1, wherein the printed circuitboard further comprises: a second conductive layer, wherein the whitecore layer is interposed between the first and second conductive layers.3. The display defined in claim 2, wherein the printed circuit boardfurther comprises: a prepreg layer, wherein the second conductive layeris interposed between the white core layer and the prepreg layer.
 4. Thedisplay defined in claim 3, wherein the printed circuit board furthercomprises: a third conductive layer, wherein the prepreg layer isinterposed between the second and third conductive layers.
 5. Thedisplay defined in claim 4, wherein the printed circuit board furthercomprises: an additional white solder resist layer, wherein the thirdconductive layer is interposed between the prepreg layer and theadditional white solder resist layer and wherein the additional whitesolder resist layer has a reflectivity of more than 80%.
 6. The displaydefined in claim 5, wherein the prepreg layer has a lower dielectricconstant than the additional white solder resist layer.
 7. The displaydefined in claim 6, wherein the additional white solder resist layer hasa lower dielectric constant than the white core layer.
 8. The displaydefined in claim 7, wherein the white core layer has a lower dielectricconstant than the white solder resist layer.
 9. The display defined inclaim 5, wherein the printed circuit board further comprises: aconductive shield attached to a lower surface of the additional whitesolder resist layer using a layer of adhesive.
 10. The display definedin claim 5, wherein the white core layer is thicker than the firstconductive layer, the white solder resist layer, the second conductivelayer, the prepreg layer, the third conductive layer, and the additionalwhite solder resist layer.
 11. The display defined in claim 5, whereinthe additional white solder resist layer has a lower thickness than thewhite solder resist layer.
 12. The display defined in claim 1, whereineach light source is mounted to the printed circuit board in arespective rectangular opening in the white solder resist layer.
 13. Adisplay, comprising: a plurality of pixels; and a backlight configuredto produce backlight illumination for the plurality of pixels, whereinthe backlight comprises: a substrate; a plurality of light sourcesmounted on the substrate; and a color conversion layer that receiveslight from the plurality of light sources, wherein the color conversionlayer comprises: a phosphor layer; a partially reflective layer; and ananti-static layer, wherein the phosphor layer is interposed between theanti-static layer and the partially reflective layer.
 14. The displaydefined in claim 13, wherein the color conversion layer furthercomprises: a plurality of protrusions, wherein the anti-static layer isinterposed between the plurality of protrusions and the phosphor layer.15. The display defined in claim 14, wherein the plurality ofprotrusions is a plurality of pyramidal protrusions.
 16. The displaydefined in claim 14, wherein the color conversion layer furthercomprises: a base film that is interposed between the phosphor layer andthe plurality of protrusions.
 17. The display defined in claim 16,wherein the anti-static layer is interposed between the base film andthe plurality of protrusions.
 18. The display defined in claim 16,wherein a static decay time at a bottom surface of the base film is lessthan 10 seconds.
 19. A display, comprising: a printed circuit board; anarray of light sources mounted on the printed circuit board in an activearea; and a plurality of electronic components mounted on the printedcircuit board in an inactive area, wherein the plurality of electroniccomponents includes a first electronic component having first and secondopposing sides connected by third and fourth opposing sides and whereinthe first electronic component is surrounded by encapsulant on thefirst, second, and third sides but not the fourth side.
 20. The displaydefined in claim 19, wherein the plurality of electronic componentsincludes: a second electronic component, wherein the fourth side of thefirst electronic component is adjacent to the second electroniccomponent; and a third electronic component that is surrounded byadditional encapsulant on three sides and is not surrounded by theadditional encapsulant on a side adjacent to the second electroniccomponent.